Preheat the oven to 350°F (175°C).

Chop the onion and dice the bell peppers, and gather all remaining ingredients.

In a large mixing bowl, combine ground beef, ground pork, breadcrumbs, Parmesan cheese, parsley, chopped onion, ketchup, eggs, garlic powder, salt, and pepper; mix until just combined.

On a parchment-lined surface, shape the meat mixture into a rectangle about 1 inch thick.

Sprinkle the shredded mozzarella cheese and diced bell peppers evenly over the meat rectangle.

Carefully roll the meatloaf from one long side to the other, sealing the edges to encase the filling.

Place the rolled meatloaf seam-side down in a loaf pan, cover with aluminum foil, and bake for 45 minutes.

Remove the foil and bake for an additional 15 minutes or until a golden crust forms; the internal temperature should reach 160°F (70°C).

Let the meatloaf rest for 10 minutes before slicing to allow juices to redistribute.