Preheat your oven to 375°F (190°C). Gather your mixing bowls and prepare a baking sheet or parchment paper.

In a large bowl, combine ground beef, ground Italian sausage, breadcrumbs, beaten eggs, garlic powder, onion powder, and Italian seasoning. Season with salt and pepper to taste. Mix gently until just combined.

In a separate bowl, mix mozzarella cheese, Parmesan cheese, and fresh spinach, if using. Ensure all ingredients are evenly distributed.

Flatten the meat mixture into a rectangle about ½ inch thick on parchment paper or a baking sheet.

Spread the cheese filling evenly over the meat mixture, leaving about an inch around the edges.

Roll the meatloaf from one edge to the opposite side, jelly-roll style, ensuring the filling is enclosed.

Place the rolled meatloaf seam-side down in a baking pan or on a baking sheet.

Bake for 45-50 minutes, checking for an internal temperature of 160°F (71°C) with a meat thermometer.

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

Allow the meatloaf to rest for 10 minutes after removing it from the oven, then slice into portions and serve.