Spaghetti Squash Casserole
See my guide on how to use an Instant Pot.
This Spaghetti Squash Casserole is made with ground beef, marinara sauce, cheese and tender strands of spaghetti squash. It’s a delicious dinner idea that will have everyone going back for seconds!
As I was testing the recipe for this spaghetti squash casserole, it quickly became one of our favorite dinners. I had high hopes that this casserole would turn out to be the flavorful, cheesy and nutritious comfort food I was craving, and it far exceeded my expectations. It’s so good, you’ll hardly know you are eating squash, not pasta!
The flavor profile of this easy casserole recipe is similar to our favorite homemade lasagna recipe or a baked spaghetti. It’s made with a quick Bolognese sauce and two kinds of cheese. To make the meat sauce, I use one of my favorite kitchen shortcuts: store-bought marinara. This saves time and effort on a busy weeknight, although you can certainly use homemade marinara sauce if you prefer.
I usually cook the spaghetti squash in the oven before making this recipe, and you can read my tips for how to cook spaghetti squash. You can also cook the spaghetti squash in an Instant Pot to make this spaghetti squash recipe.
Spaghetti Squash Casserole Ingredients
- Spaghetti Squash: A medium spaghetti squash will give you the perfect amount of squash for this recipe.
- Olive Oil, Salt & Pepper: These are used to season the spaghetti squash before cooking it in the oven. You’ll also use salt and pepper to season the meat sauce.
- Ground Beef: Ground beef adds protein to the casserole to make it a filling meal.
- Onion & Garlic: These aromatic ingredients provide the first layer of flavor in this recipe.
- Bell Pepper: To sneak in extra veggies! Use any color of bell pepper that you have on hand.
- Marinara Sauce: Since marinara sauce is already seasoned, it brings an extra layer of flavor to the casserole.
- Italian Seasoning: This dish has Italian flavors, so adding Italian seasoning is the perfect way to season the sauce.
- Parmesan Cheese & Mozzarella Cheese: I love using a combination of these two cheeses because the mozzarella melts especially well and the Parmesan adds an extra pop of salty, cheesy flavor.
Find the full printable recipe with ingredient amounts and instructions in the recipe card below.
How to Make Spaghetti Squash Casserole
First, we need to cook the spaghetti squash. Cut the squash in half and scoop out the seeds. (You can discard the seeds or save them for roasting like roasted pumpkin seeds.) Rub the squash with olive oil and season it with salt and pepper. Place the squash halves cut side down on a parchment paper lined baking sheet and bake in the oven for 30-40 minutes, until tender. Once cool enough to handle, use a fork to separate the strands of squash and scoop them out of the skin.
To prepare the casserole, brown the ground beef in a large skillet on the stove. Then add the chopped onion and bell pepper and cook until softened. Stir in the salt, pepper and minced garlic and cook for 30 seconds, stirring.
Stir in the marinara sauce and Italian seasoning. Cook at a low simmer for 5 minutes to allow the flavors to develop. Then remove the pan from the heat. Stir in the spaghetti squash and grated Parmesan cheese. Transfer the mixture to a casserole dish.
Bake for 10 minutes, then sprinkle with shredded mozzarella cheese and bake for 10-15 more minutes, until the casserole is hot and bubbly and the cheese is melty.
- Cutting the spaghetti squash in half lengthwise, from stem end to base end, yields shorter strands of squash which are perfect for this casserole recipe. See more about how to cut spaghetti squash.
- Feel free to use ground turkey instead of ground beef for a leaner casserole.
- Using store-bought marinara sauce makes this recipe especially quick and easy. You can substitute 3 cups of homemade Marinara Sauce if you prefer.
- To make this squash casserole faster to prep on a weeknight, you can cook the squash up to 2 days ahead of time and refrigerate it in an airtight container until you are ready to use it in this recipe.
- If you’re serving spaghetti squash skeptics and you don’t need the meal to be gluten-free, you can replace half of the spaghetti squash in this recipe with spaghetti pasta. This is a great way to introduce this versatile squash into your diet.
Storage and Reheating Tips
This casserole reheats well and is delicious on the second and third day! Store leftovers in a covered dish in the refrigerator for up to 3 days. It is easiest to reheat individual servings in the microwave. You can also reheat this spaghetti squash casserole in a 350° F oven. Take it out of the refrigerator for about 15 minutes to take the chill off. Then cover the dish with foil and bake for 15-20 minutes, or until hot.
More Healthy Dinner Ideas
Spaghetti Squash Casserole
- 1 medium spaghetti squash
- 1 tablespoon olive oil
- salt and pepper
- 1 pound ground beef
- 1 cup finely chopped yellow onion
- 1 bell pepper, any color, chopped
- 3 cloves garlic, minced
- 25 ounce jar marinara sauce*
- 1 teaspoon Italian seasoning
- ⅓ cup grated Parmesan cheese
- 1 cup shredded mozzarella cheese
- chopped fresh parsley or basil, optional, for serving
Cook the Spaghetti Squash
- Preheat oven to 400° F. Line a rimmed baking sheet with parchment paper.
- Slice a small amount off of the base and stem ends of the spaghetti squash. Then stand the squash up on one of the flat ends and carefully use a sharp knife to cut the squash in half lengthwise (from the stem end to the base). Be sure to keep your hand that is not holding the knife above the knife for safety. Scoop out the seeds (discard or set aside for roasting).
- Drizzle the olive oil over the inside of the squash and rub over the squash to distribute. Sprinkle with salt and pepper. Place the squash halves cut side down on the prepared baking sheet.
- Roast squash in the preheated oven for 30-40 minutes, until just tender when pierced with a fork or knife. Try not to overcook the squash, as it is better to have the strands al dente than mushy.
- Let the squash cool until it is cool enough to handle. Then use a fork to separate the squash into strands. Reduce the oven temperature to 375° F.
Make the Casserole
- While the squash cooks, you can begin preparing the casserole. Heat a large skillet over medium-high heat on the stove. Add the ground beef to the hot pan and cook, crumbling with a spoon, until just browned (the meat will continue to cook when you add the onion and bell pepper to the pan). Drain off any excess grease.
- Add the onion and bell pepper to the pan and cook a for about 3 minutes, until softened, stirring often. Stir in ½ teaspoon salt, ⅛ teaspoon black pepper and the minced garlic and cook for 30 seconds, stirring.
- Stir in the marinara sauce and Italian seasoning. Reduce the heat to a low simmer and cook for 5 minutes, stirring occasionally.
- Remove the pan from the heat. Stir in the spaghetti squash strands, followed by the grated Parmesan cheese.
- Lightly grease a 9x13-inch baking dish with cooking spray. Transfer the contents of the skillet to the baking dish.
- Bake at 375° F for 10 minutes, then sprinkle with the mozzarella cheese and bake for 10-15 more minutes, until casserole is hot and bubbly on the sides and cheese is lightly browned. Serve garnished with chopped fresh parsley or basil, if desired.
- You may substitute ground turkey for the ground beef.
- 3 cups of homemade marinara sauce may be substituted for the 25 ounce jar of sauce.