Preheat your oven to 350°F (175°C). Grease a 9x13 inch casserole dish with cooking spray or olive oil.
In a large bowl, combine the ground beef, ground turkey, breadcrumbs, grated Parmesan cheese, milk, ketchup, egg, garlic powder, onion powder, salt, and black pepper. Mix until just combined; do not overmix.
Fold in the diced bell peppers and corn, ensuring they are evenly distributed throughout the meat mixture.
Transfer the meat mixture into the prepared casserole dish, shaping it into a loaf shape.
Bake in the preheated oven for 45-50 minutes, until the meat is cooked through and the internal temperature reaches 160°F (70°C).
Remove the casserole from the oven and sprinkle the shredded mozzarella cheese on top. Return to the oven and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
Let the casserole rest for 10 minutes before slicing. Garnish with fresh parsley before serving.
Notes
Serve slices with extra ketchup on the side for dipping.