1. In a medium bowl, combine the chicken (or turkey), eggs, onion, breadcrumbs, Italian seasoning, garlic powder, 1/2 cup marinara and 1/2 cup cheese (it's easiest to just use your hands to do this).
2. Spray an 8x5-inch loaf pan with nonstick spray (metal or glass- see notes below). Scoop the meatloaf mixture into the pan and smooth the top. Spread the remaining 1/2 cup of marinara sauce over the top. Sprinkle remaining 1 cup of cheese on top. Put the pan in a 6-quart slow cooker and place the lid on top. Cook for 7 to 8 hours on low (or 4 hours on high).