1. Thoroughly mix the turkey, onion, concentrated broth and black pepper in a medium bowl. Shape the turkey mixture into 4 (1/2-in. thick) burgers.
2. Heat the oil in a 12-in. nonstick skillet over medium-high heat. Add the burgers and cook until well browned on both sides. Reduce the heat to low. Cover and cook until the burgers are cooked through. Top the burgers with the cheese and cook until the cheese is melted.
3. Serve the burgers on the buns.