01 - Preheat oven to 375°F. Line a loaf pan with parchment paper or lightly grease it.
02 - In a large mixing bowl, combine the ground chicken, Parmesan, mozzarella, onion, garlic, parsley, breadcrumbs, egg, milk, marinara sauce, Italian seasoning, salt, and pepper. Mix until just combined, being careful not to overwork the meat.
03 - Transfer the mixture to the prepared loaf pan and gently press it in to form an even, uniform loaf.
04 - Spread a few additional tablespoons of marinara sauce evenly over the top for extra flavor and moisture.
05 - Bake for 45 to 50 minutes, or until the meatloaf is golden, set, and the internal temperature reaches 165°F.
06 - Let the meatloaf rest for 10 minutes before slicing. Serve with additional warm marinara sauce on the side if desired.