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Caramelized Onion Spaghetti Squash Casserole

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You won’t miss the dairy when you serve this casserole! The eggs in this recipe create a creamy and “cheesy” crust so divine that you might actually think you put mozzarella right in there.

MORE: Find Tons of Spaghetti Squash Recipes

This recipe can be made ahead and even frozen, it will be your new go to healthy side dish. 

Caramelized Onion Spaghetti Squash Casserole
  • Duration
  • Cook Time
  • Prep Time
  • 6Servings


  • 1 medium spaghetti squash
  • Extra-virgin olive oil, such as Colavita
  • Kosher salt
  • Freshly cracked black pepper
  • 2 medium yellow onions, sliced
  • 1 (8 ounce) box mushrooms, sliced
  • ½ cup vegetable broth, white wine or water
  • 1 cup tomato sauce
  • 1 teaspoon garlic powder
  • 3 eggs, whisked


1. Preheat the oven to 400°F, line a baking sheet with baking paper and grease a 8x8 casserole dish with olive oil.

2. Cut spaghetti squash in half lengthwise, scoop out seeds, season with olive oil, salt and pepper and place cut-side down on the prepared baking sheet. Bake for 45 minutes, until the skin of the squash is fork tender.

3. While squash is baking, prepare caramelized onions and mushrooms. Heat olive oil in a frying pan over medium-high heat, add onions and mushrooms. Lower the temperature to medium and cook onions and mushrooms until beginning to brown, about 10 minutes, stirring occasionally to prevent burning. Add broth, wine or water to the pan and using a flat edged wooden spoon “scrape” the bottom of the pan to pick up the brown bits. Cook onions and mushrooms for 8-10 minutes more, until there is no more liquid in the pan.

4. Remove squash from the oven, scoop out flesh and place in the prepared casserole dish. Stir in caramelized onions, mushrooms, tomato sauce, garlic powder, whisked eggs and season with ½ teaspoon salt and ½ teaspoon pepper.  Mix everything together until you can no longer see eggs.

5. Bake uncovered at 400°F for 1 hour, until the top of the casserole has formed a golden crust that is brown around the edges. Let rest for 10 minutes before serving.

For more recipes with Spaghetti Squash click here