Spread the salad dressing on one side of half of the bread slices. Place bread slices, dressing side up, on the unheated rack of a broiler pan.
Layer the zucchini, tomato, sweet pepper, and red onion on bread; top with sauerkraut. Place the cheese on the remaining bread slices. Place bread, cheese side up, on rack.
Broil about 4 inches from the heat about 1 minute or until cheese is melted. Invert the cheese-topped bread slices over the vegetables. Broil about 1 minute more or until bread is lightly toasted, turning once. Makes 2 servings.