Shape beef into twelve 1-in. patties. Place on a microwave-safe plate lined with paper towels. Cover with another paper towel; microwave on high for 1 minute until meat is no longer pink. Cut each slice of cheese into fourths; set aside., Using a 1-in. round cookie cutter, cut out 6 circles from each slice of bread. Spread half the bread circles with dressing. Layer with burgers, cheese, onions, pickles and tomatoes. Top with remaining bread circles; secure with toothpicks.