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. Mix gently until just combined.

In a separate bowl, mix together mozzarella cheese, Parmesan cheese, and spinach (if using).

Lay out a piece of parchment paper and transfer the meat mixture onto it, shaping it into a rectangle about 1-inch thick.

Spread the cheese filling evenly over the shaped meat mixture, leaving a small border.

Carefully roll the meat mixture up using the parchment paper, tucking the filling in as you go. Place seam-side down in a baking pan.

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

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

Let the meatloaf rest for 10 minutes before slicing.

Slice and serve with additional marinara sauce, garlic bread, or a light salad.