1Heat gas or charcoal grill. In medium bowl, mix all ingredients except buns and onions. Shape mixture into 4 patties, about 1/2 inch thick.
2Carefully brush vegetable oil on grill rack. Place patties on grill rack over medium heat. Cover grill; cook patties 12 to 15 minutes, turning once, until thermometer inserted in center of patties reads 165°F. Add buns, cut sides down, to side of grill for last 4 minutes of grilling. Serve patties on buns with grilled or raw onion rings.