PREHEAT broiler. Place bread slices in single layer on baking sheet. Broil 2 min. on each side or until golden brown on both sides.
MIX dressing and cheese. Remove 1/4 cup of the dressing mixture; set aside. Spread remaining dressing mixture evenly onto toast slices.
COMBINE tomatoes, onions and reserved 1/4 cup dressing mixture; spoon onto toast slices just before serving.