1Heat gas or charcoal grill. In medium bowl, mix beef, parsley, 2 tablespoons of the dressing and the peppered seasoned salt. Shape mixture into 4 patties, about 1/2 inch thick.
2Place patties on grill over medium heat. Cover grill; cook 12 to 15 minutes, turning once, until meat thermometer inserted in center of patties reads 160ºF. Add onion slices to grill for last 8 to 10 minutes of cooking, brushing with 2 tablespoons of the dressing and turning once, until crisp-tender.
3In small bowl, toss lettuce, remaining 1/4 cup dressing and the cheese. Layer lettuce mixture, burger and onion in each bun.