Preheat your oven to 400°F (200°C) and coat a 9x13 inch casserole dish with olive oil.

In a skillet over medium heat, warm a splash of olive oil. Cook ground beef and Italian sausage until halfway browned, about 5-7 minutes. Add diced onion and sauté for about 3 minutes until softened.

Stir in minced garlic, Italian seasoning, salt, pepper, and optional red pepper flakes, cooking for 1 more minute.

Pour in marinara sauce and let it simmer for about 10 minutes.

In a mixing bowl, combine ricotta cheese, softened cream cheese, chopped parsley, and grated Parmesan. Season with salt and pepper.

Layer half of the cooked spaghetti squash in the casserole, then half of the meat sauce, and half of the cheese mixture. Repeat layers.

Sprinkle grated mozzarella cheese on top and bake for 20-25 minutes until cheese is bubbly and golden brown.

Let the casserole rest for 10 minutes before serving. Garnish with fresh parsley or basil.