Creating this Meatball Sub Casserole is simple when following these clear steps:

1. Preheat the Oven: Start by preheating your oven to 375°F (190°C).
2. Make the Meatballs: In a large bowl, combine ground beef, Italian sausage, breadcrumbs, Parmesan cheese, egg, parsley, salt, and pepper. Mix until well combined.
3. Shape Meatballs: Form the mixture into medium-sized meatballs and set them aside.
4. Brown Meatballs: In a large skillet over medium heat, add olive oil. Cook the meatballs until browned on all sides (approx. 5-7 minutes).
5. Add Marinara Sauce: Pour the marinara sauce over the meatballs and let it simmer for about 10 minutes.
6. Prepare the Bread: While the meatballs are simmering, slice the Italian bread into halves. Mix the minced garlic with olive oil and brush it over the bread slices. Arrange them in a single layer in a baking dish.
7. Layer the Casserole: Once the meatballs are done, remove them from the skillet. Distribute them evenly over the toasted bread. Pour the marinara sauce over the meatballs.
8. Add Cheese: Sprinkle a generous amount of mozzarella cheese on top of the meatballs and sauce.
9. Bake the Casserole: Cover the casserole dish with aluminum foil and bake for 20 minutes. Remove the foil and bake for an additional 10-15 minutes, until the cheese is bubbly and golden brown.
10. Let it Rest: Once out of the oven, let the casserole sit for a few minutes before serving.

Following these steps will help you create a scrumptious Meatball Sub Casserole that indulges your taste buds!