1. Preheat broiler to high.
2. Place graham cracker squares on a foil-lined baking sheet. Divide chocolate evenly among 4 squares; top evenly with banana slices. Spread 1 tablespoon marshmallow creme on each of 4 remaining squares. Broil 1 1/2 minutes or until chocolate just begins to melt and marshmallow creme lightly browns. Carefully top banana with the marshmallow-topped squares.