1. Combine breadcrumbs, onion, olive oil, salt, pepper, and ground turkey in a medium bowl. Mix with hands until well-blended. Form mixture into four patties, about 1/2-inch thick. 2. Heat a grill pan or griddle over medium-high heat. Place patties on grill pan. Cook 3 to 5 minutes per side, until completely cooked through. The juices should run clear when poked with a knife. Once patties are flipped, top each with a slice of cheese. Transfer burgers to warmed buns. Serve immediately with choice of toppings.