Creating Spaghetti Squash Meatball Casserole is simple if you follow these easy steps:

1. Preheat the Oven: Preheat your oven to 375°F (190°C).
2. Cook the Spaghetti Squash: Cut the spaghetti squash in half lengthwise and scoop out the seeds. Place the halves cut side down on a baking sheet. Bake for 30-40 minutes until tender.
3. Prepare the Meatballs: In a large bowl, combine the ground meat, breadcrumbs, Parmesan cheese, parsley, egg, garlic, onion powder, Italian seasoning, salt, and pepper. Mix until fully combined.
4. Form Meatballs: Shape the mixture into meatballs, about 1-1.5 inches in diameter, and place them on a baking sheet.
5. Bake the Meatballs: Bake meatballs in the preheated oven for 20-25 minutes or until cooked through.
6. Scrape the Squash: Once the spaghetti squash is cooked, let it cool slightly. Use a fork to scrape out the strands and place them in a large mixing bowl.
7. Combine Ingredients: Add the marinara sauce and cooked meatballs to the spaghetti squash. Stir until well combined.
8. Transfer to Casserole Dish: Pour the mixture into a greased casserole dish, spreading it evenly.
9. Top with Cheese: Sprinkle the shredded mozzarella cheese over the top of the casserole.
10. Bake Again: Return the casserole to the oven and bake for an additional 20 minutes, or until the cheese is melted and bubbly.

These straightforward steps will guide you in making a delicious Spaghetti Squash Meatball Casserole that you and your family will enjoy.