Preheat your oven to 375°F (190°C). Prepare a baking sheet or loaf pan lined with parchment paper.

In a large mixing bowl, combine the ground beef, ground Italian sausage, breadcrumbs, eggs, garlic powder, onion powder, Italian seasoning, salt, and pepper. mix gently until just combined.

In a separate bowl, mix the mozzarella cheese, Parmesan cheese, and spinach if using.

On a large piece of parchment paper, flatten the meat mixture into a rectangular shape, about 1 inch thick.

Spread the cheese filling across the center of the flattened meat mixture, leaving a border around the edges.

Roll the meat mixture tightly using the parchment paper, sealing the edges to prevent leaks.

Bake for 45-50 minutes until the internal temperature reaches 160°F (71°C).

In the last 10 minutes of baking, spread marinara sauce on top and return to the oven.

Let the meatloaf rest for about 10 minutes before slicing and serving with extra marinara, mashed potatoes, or salad.