Combine ground beef, breadcrumbs, milk, and seasonings, mixing well; shape into 6 patties about 3/4-inch thick.
Place patties on a rack in broiler pan. Broil 5 inches from heat for 5 minutes on each side or until burgers reach desired doneness.
Place a slice of cheese on each burger and broil 20 seconds or until cheese melts.
Slice the bread legnthwise, then into 6 equal portions. Place bacon on bottom half of bread portions; top with cheeseburgers, tomato, onion, and top half of bread portions. Serve with ketchup and mustard.