Preheat your oven to 375°F (190°C).

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

In a separate bowl, mix together the mozzarella cheese, parmesan cheese, and optional spinach until well incorporated.

Transfer the meat mixture onto parchment paper and shape into a rectangle about 1/2 inch thick.

Spread the cheese and spinach filling evenly across the meat rectangle, leaving roughly an inch clear around the edges.

Starting from one long edge, carefully roll the meat mixture tightly into a log.

Place your rolled meatloaf on a lined baking sheet and pop it in the preheated oven. Let it bake for 45-50 minutes, or until it reaches an internal temperature of 160°F (71°C).

About 10 minutes before the end of baking, top it with marinara sauce and return to the oven to finish baking.

Once removed from the oven, let it rest for about 10 minutes before slicing.

Slice the meatloaf into thick pieces and serve warm with your favorite sides.