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Spaghetti squash noodles can be substituted in many other pasta dishes or served topped with regular pasta sauce saving you loads of carbs — so what’s not to love?!
My Spaghetti Squash Casserole combines fresh “squaghetti” noodles with sautéed spinach, red bell pepper, and garlic plus three kinds of cheese to create a rich, yet delicate dish.
This creamy Spaghetti Squash Casserole is a cheesy vegetarian, keto-friendly, low-carb, gluten-free casserole. That covers just about all the bases!
Looking for more vegetarian main dishes? My Easy Skillet Vegetable Lasagna is loaded with zucchini, yellow squash, onions, and mushrooms and is ready in just 30 minutes! Or, you may like this Healthy Butternut Squash Soup — it’s perfectly creamy and delicious.
Spaghetti Squash Casserole: behind the recipe
Confession time. The first time I made this recipe was my very first experience cooking spaghetti squash. Truth! I’m not sure why it’s took me so long to try this vegetable, but let me tell you that this first time will not be my last.
Unlike other veggies that you spiralize to make noodles, once cooked the flesh of a spaghetti squash can be separated into spaghetti-like strands (or squaghetti as I like to call it) simply by scraping it out with a fork.
One three-pound squash will make enough squaghetti to equal around a pound of pasta noodles — a great alternative when you are watching your carb intake!
Key ingredients and substitutions
- Spaghetti squash — Choose a squash that doesn’t have cracks or spots on its skin and be sure the stem is not withered and dry.
- Red bell pepper — Any color bell pepper will work, but I like the sweetness of red bell peppers.
- Onion — A yellow or sweet onion along with fresh garlic adds the aromatic flavors to this dish. To make it heartier, toss in mushrooms, sundried tomatoes, or any other veggie you find in your fridge.
- Spinach — I use fresh baby spinach, but you can also use frozen chopped spinach. Just be sure to thaw and squeeze out any liquid before adding to the casserole.
How to make spaghetti squash casserole
STEP 1 | Cook the squash
- Cut the spaghetti squash in half length-wise and use a large spoon to scrape and scoop out the seeds.
- Lay the squash cut side down in a baking dish and pour in 1/2 cup water.
- Bake the squash until it is tender and easily be pierced with a fork.
- Remove the squash from the pan and let rest until it is cool enough to handle.
- Gently scrape all the flesh away from the rind/peel with a fork.
- Cook spaghetti squash in the instant pot – Add one inch of water to the Instant Pot and insert the steamer basket. Lay the squash in the basket (not in the water) and lock the lid with the valve set to vent. Pressure cook for 5 minutes, then quick release the steam by carefully opening the vent. Remove the squash and let cool.
STEP 2 | Sauté vegetables
- Sauté diced onions and red bell pepper until tender, then add minced garlic and cook another minute until fragrant.
- Toss in fresh spinach and cook until wilted.
STEP 3 | Add cheese and bake
- Add a block of softened cream cheese to the pan with the veggies and stir until melted.
- Gently stir in the spaghetti squash and transfer the mixture in a lightly greased casserole dish.
- Top with mozzarella and parmesan cheese and bake until hot, bubbly, and the cheese has a golden crust.
- After removing the casserole from the oven, allow it to set for at least 15 minutes. Then, you’ll be able to cut it into squares and serve like a lasagna.
Frequently asked questions
To reheat the casserole, place a serving on a microwave-safe plate and heat for 1 1/2 minutes in the microwave until warmed through.
To serve spaghetti squash casserole as a more complete meal, add cooked and crumbled Italian sausage or shredded rotisserie chicken before you bake. Both are delicious options!
More delicious vegetable recipes
- Zoodle Ratatouille is a composition of seasonal vegetables—zucchini, onions, sweet bell peppers, and tomatoes—cooked with olive oil and garlic.
- Broccoli Rice and Cheese Casserole is a delicious side dish for barbecue chicken, pork chops, or even meatloaf. A creamy rice dish using fresh broccoli and mushrooms, this casserole also uses both cheddar and Parmesan cheese for extra cheesy goodness!
- Grilled Corn and Mushroom Risotto starts with grilling fresh corn, mushrooms, and poblano chili peppers to create this creamy and hearty one-dish meal.
- Balsamic Roasted Parsnips and Carrots are topped with a feta cheese “salad” of lemon, parsley, and dried cherries.
- Roasted Spaghetti Squash with Marinara — low-carb spaghetti option!
- Crunchy Oven-Fried Okra — My “fried” okra recipe uses a fraction of the oil used when pan frying which is an added health benefit!
- More side dish recipes!
Creamy Spinach Spaghetti Squash Casserole
- 1 3 lb. spaghetti squash
- 1/2 cup water
- 1 teaspoon olive oil
- 1/2 large red bell pepper diced
- 1/2 cup diced sweet onion
- 1 clove garlic minced
- 4 cups spinach chopped
- dash of nutmeg
- 1 teaspoon salt
- 1/2 teaspoon pepper
- 8 oz. cream cheese softened
- 1 cup mozzarella cheese
- 1/4 cup parmesan cheese
- Preheat oven to 400 degrees.
- Slice spaghetti squash in half length-wise. Scoop out seeds and place cut side down in a glass baking dish. Pour 1/2 cup water into dish and bake for about 30-35 minutes. With a fork gently shred the pulp from the inside of the squash and set aside.Reduce oven heat to 375 degrees.
- On top of stove, heat olive oil in a large skillet over medium heat. Add the onion and red bell pepper. Sauté about 5 minutes, until tender. Add the garlic and cook until fragrant, about 1 minute.
- Add the spinach to the skillet and season with the nutmeg, salt, and pepper. Cook and stir until the spinach is wilted.
- Gently stir in the cream cheese until melted. Add the spaghetti squash and stir until combined.
- Pour the mixture into a casserole dish that is lightly coated with cooking spray. Top with the mozzarella and parmesan cheese. Bake at 375 degrees for 30 minutes, or until bubbly and cheese is lightly browned.
- After removing the casserole from the oven, allow it to set for at least 15 minutes if you’d like to cut it into squares to serve like lasagna.
- To reheat the casserole, place a serving on a microwave-safe plate and heat for 1-1/2 minutes in the microwave.
- Cut the spaghetti squash in half length-wise.
- Use a large spoon to scrape and scoop out the seeds.
- Add one inch of water to the Instant Pot and insert the steamer basket.
- Lay the squash in the basket (not in the water) and lock the lid and turn the valve to vent.
- Pressure cook for 5 minutes. When the pot beeps, hit cancel.
- Quick release the steam by carefully opening the vent.
- Remove squash and allow it to cool enough to handle.
- Use a fork to gently scrape all the flesh away from the rind/peel.
About Sheila Thigpen
Recipe Developer, Food Photographer, Food Writer
Sheila Thigpen is the publisher of Life, Love, and Good Food — a Southern food blog — and the author of Easy Chicken Cookbook and The 5-Ingredient Fresh and Easy Cookbook. After 20+ years in the publishing industry, she retired in 2018 to focus on her own creative endeavors full time. She and her husband live near the beautiful Smoky Mountains and have a precious little granddaughter who has stolen their hearts. As an influencer, Sheila has collaborated with brands like Creamette, Kroger, HERSHEY’S, Hamilton Beach, Garafalo Pasta, OXO, Smithfield, Valley Fig Growers, and more.