Preheat your oven to 375°F (190°C).

In a large bowl, combine ground beef, ground Italian sausage, breadcrumbs, eggs, garlic powder, onion powder, Italian seasoning, salt, and pepper. Mix gently.

In another bowl, mix together the mozzarella cheese, Parmesan cheese, and optional spinach.

On a sheet of parchment paper, flatten the meat mixture into a large rectangle, about 1 inch thick. Lay the cheese filling evenly in the center.

Starting from one end, carefully roll the meat mixture around the cheese filling, tucking it in as you go.

Transfer the rolled meatloaf onto a baking sheet or into a loaf pan, placing it seam-side down. Bake for 45-50 minutes.

During the last 10 minutes of baking, spoon marinara sauce over the top of the meatloaf.

Once baked, let the meatloaf rest for at least 10 minutes before slicing.

Slice into thick pieces and serve with additional marinara sauce and sides like mashed potatoes or roasted vegetables.