Prepare grill for medium-high heat. In large bowl, combine beef, salt and pepper; mix gently. Form beef into 4 patties; grill until desired doneness. Top each burger with 2 slices cheese, if desired. In microwave-safe bowl, microwave peanut butter 30 seconds. Place patties on bottom halves of buns. Generously spread warm peanut butter on each patty. Top with 2 to 4 slices bacon; cover with top halves of buns.