Preheat the oven to 350 degrees F (175 degrees C).
Combine turkey, bread crumbs, eggs, onion, Parmesan cheese, and pepper in a large bowl. Fold in 1 cup marinara sauce.
Pat turkey mixture firmly into a 8x4-inch loaf pan using wet hands. Pour remaining marinara sauce on top.
Bake in the preheated oven until meatloaf is no longer pink in the center, about 1 hour. An instant-read thermometer inserted into the center should read at least 160 degrees F (70 degrees C). Let stand 20 minutes before cutting.
