How to Make It
Combine first 3 ingredients, stirring well; shape into 4 (1/2-inch-thick) patties.
Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Place meat patties and onion slices on rack; grill, covered, 5 minutes on each side or until meat is done. Place 1 pattie and 1 onion slice on bottom half of each roll. If desired, add mustard and ketchup. Top with remaining roll half.
Cooking Light 5-Ingredient 15-Minute Cookbook