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 gently until just combined, being careful not to overwork the meat.
03 - Transfer the mixture to the prepared loaf pan, gently pressing it down to form an even, compact loaf.
04 - Spread a few additional tablespoons of marinara sauce evenly over the top of the loaf for extra flavor and moisture.
05 - Bake for 45 to 50 minutes, or until the meatloaf is golden brown, firmly set, and the internal temperature reaches 165°F when checked with a meat thermometer.
06 - Remove from the oven and let the meatloaf rest for 10 minutes before slicing. Serve with additional warm marinara sauce on the side if desired.