This Spaghetti Squash Casserole is healthy comfort food at its best — cozy, satisfying, and made with simple, real ingredients. It delivers the familiar flavors of a classic pasta bake but swaps the pasta for tender roasted spaghetti squash. Ground beef and mushrooms simmer in a savory tomato sauce with herbs and a splash of balsamic vinegar, then the mixture is combined with the shredded squash and finished with melted mozzarella for a warm, homey dinner.
This Spaghetti Squash Casserole is a vegetable-forward take on a baked pasta dish. Roasted spaghetti squash provides tender strands that absorb the rich tomato-beef sauce, while mushrooms add an earthy, meaty texture. A moderate amount of cheese binds everything and gives that golden, bubbly finish you expect from a casserole.
After the squash is cooked, the casserole comes together in one skillet: brown the meat and vegetables, add sauce ingredients, stir in the squash, top with cheese and bake until bubbly. The method keeps cleanup simple and makes this a practical meal for busy weeknights.
This casserole is similar in spirit to a spaghetti squash lasagna, but lighter — it uses fewer layers of cheese and is assembled in a single pan rather than baked inside halved squash.
One helpful time-saver: cook the spaghetti squash a day or two ahead of time. Stored in the refrigerator, the cooked squash makes the final assembly fast and stress-free.
Pair this casserole with a crisp green salad or roasted vegetables for a balanced plate.
Why you’ll love this recipe
- Low-carb and high-protein: swapping pasta for spaghetti squash reduces carbs while keeping the meal hearty with ground beef.
- Veggie-forward comfort: you get the cozy satisfaction of a baked pasta dish with a larger portion of vegetables.
- Simple and quick once squash is cooked: the stovetop portion takes just minutes, then a brief bake finishes the dish.
- Make-ahead friendly: roast the squash up to 48 hours in advance to cut active prep time on busy evenings.
Recipe ingredients
The ingredient list is straightforward and flexible. Use the quantities below or adjust to your taste.
- Spaghetti squash. About 2 lbs. yields roughly 3 cups cooked and shredded squash. Roasting is my preferred method because it reduces excess moisture and promotes light caramelization.
- Ground beef. Use 1 lb. of lean ground beef to keep the casserole flavorful without excess fat.
- Aromatics. Onion and garlic form the flavor base.
- Mushrooms. Baby bella or cremini mushrooms add savory depth and bulk; omit if you prefer.
- Tomato sauce and diced tomatoes. These create a saucy base that keeps the casserole moist—fire-roasted diced tomatoes add a nice smoky note.
- Tomato paste. Helps thicken the sauce and deepen tomato flavor.
- Dried herbs. Italian seasoning is a convenient option; substitute dried basil, thyme, or herbes de Provence if desired.
- Balsamic vinegar. A splash brightens and rounds the sauce—optional but recommended for depth.
- Mozzarella cheese. Use part-skim or whole-milk and grate it yourself for the best melt.
See the recipe card below for exact quantities and step-by-step instructions.
Swaps & Variations
- Lower fat: Use part-skim mozzarella or reduce the cheese amount.
- Different protein: Ground turkey, chicken or Italian sausage can be used in place of beef.
- Vegetarian: Omit the meat and add extra vegetables such as diced bell pepper, zucchini, or a can of beans; stir in spinach or kale at the end to wilt.
- Dairy-free: Skip the cheese or use a plant-based shredded alternative.
- Spice it up: Add red pepper flakes or a pinch of cayenne to the sauce.
How to make this recipe
This casserole is straightforward. First, cook the spaghetti squash using your preferred method (roasting is recommended for best texture). Let the squash cool slightly, then shred it with a fork and drain off any excess liquid if needed.
Preheat your oven to 400°F. In a large ovenproof skillet, heat olive oil over medium heat and brown the ground beef, breaking it up as it cooks. Add chopped onion and sliced mushrooms and cook until the mushrooms release their liquid. Stir in minced garlic, tomato paste, and dried herbs; cook for about 30 seconds to bloom the flavors.
Pour in tomato sauce and diced tomatoes, add a splash of balsamic vinegar, and bring the mixture to a simmer. Cook for a few minutes to concentrate the flavors, then season with salt and pepper to taste. Stir in the cooked spaghetti squash until evenly distributed. Top with grated mozzarella and transfer the skillet to the oven.
Bake for about 20 minutes, or until the casserole is bubbly and the cheese is golden. Let it rest for 5 minutes before serving. Garnish with freshly chopped parsley if desired.
Pro tip: Roast the squash 1–2 days ahead and drain it well before assembling to speed up weeknight dinners.
Recipe FAQs
Spaghetti squash can be cooked several ways, including oven roasting, the microwave, Instant Pot, or slow cooker. Roasting in the oven usually gives the best texture and flavor because it reduces excess moisture and adds light caramelization. After cooking, drain any excess liquid before using the squash in casseroles or other dishes.
Yes. You can assemble and bake the casserole, then cool it completely and store it in the fridge for up to three days. Reheat portions in the microwave or warm the whole dish in a moderate oven.
Serving suggestions
The casserole is hearty enough on its own, but it also pairs well with lighter sides to round out the meal:
- Serve with a crisp green salad to keep the plate balanced.
- Add extra roasted vegetables like Brussels sprouts or cauliflower for more texture and color.
- Offer crusty bread or focaccia for dipping in the sauce if you want a more indulgent meal.
Recipe notes
- Make-ahead: Cook the spaghetti squash 1–2 days ahead and drain well before assembling.
- Roasting tip: Roasting produces the best texture and flavor for the squash.
- Storage: Keep leftovers refrigerated for up to three days and reheat thoroughly before serving.
More casserole recipes you’ll love
- Cabbage and ground beef casserole
- Crock pot chicken and wild rice casserole
- Ground beef enchilada casserole
- One pot stuffed pepper casserole
Did you try this recipe? If so, please leave a review below and share a photo so others can see your version.
Spaghetti Squash Casserole
Ingredients
- 2 lbs. spaghetti squash
- 1 tbsp. olive oil
- 1 lb. lean ground beef
- 1 onion, chopped
- 8 oz. baby bella mushrooms, sliced
- 3 cloves garlic, minced
- 2 tbsp. tomato paste
- 1 tsp. Italian seasoning (or your favorite dried herbs)
- 15 oz. tomato sauce
- 15 oz. fire roasted diced tomatoes
- 1 tbsp. balsamic vinegar
- Salt and pepper, to taste
- 1.5 cups grated mozzarella cheese
- Freshly chopped parsley for garnish (optional)
Instructions
- Cook the spaghetti squash using your preferred method and allow it to cool. Shred the flesh with a fork and drain any excess liquid; you should have about 3 cups.
- Preheat the oven to 400°F. Heat the olive oil in a large ovenproof skillet over medium heat. Add the ground beef and cook for 2 minutes, breaking it into chunks.
- Add the chopped onion and sliced mushrooms. Cook until the mushrooms release their liquid and soften. Add the minced garlic, tomato paste and Italian seasoning; cook 30 seconds more.
- Stir in the tomato sauce, diced tomatoes and balsamic vinegar. Bring to a gentle boil, then reduce heat and simmer for about 5 minutes. Season with salt and pepper to taste.
- Fold in the shredded spaghetti squash until evenly combined. Sprinkle the grated mozzarella over the top.
- Bake for 20 minutes, or until the casserole is bubbly and the cheese is golden. Let rest 5 minutes before serving. Garnish with chopped parsley if desired.
Notes
- Pro tip: Cook the squash 1–2 days ahead to save time on busy nights and drain it well before assembling.
- Roasting the squash in the oven generally gives the best texture and flavor.
- The casserole can be assembled ahead and baked when needed.
- Leftovers keep in the refrigerator for up to 3 days.
Nutrition
Nutrition is estimated and provided for guidance only.