In a small bowl, combine the first five ingredients. Crumble beef over mixture and mix well. Shape into four thin patties. Sprinkle cheese over two patties; top with remaining patties and press edges firmly to seal.
Grill, covered, over medium heat for 6 minutes on each side or until a meat thermometer reads 160° and juices run clear. Serve on buns with lettuce and tomato if desired. Yield: 2 servings.