Combine first nine ingredients; mix lightly. Shape into four 3/4-in.-thick patties. Press patties into flour to lightly coat both sides., In a large cast-iron or other heavy skillet, cook burgers over medium heat until a thermometer reads 160°, 4-5 minutes per side. Layer bun bottoms with salad dressing, lettuce, burgers, cheese, onion and tomato slices. Replace bun tops.