Toast bread and let cool. Combine mashed banana, cream cheese, and cocoa powder in a medium bowl. Spread some of the mixture over each toasted bread slice. Place slices on a cookie sheet. Layer banana slices on top of cream cheese mixture. Brush bananas with melted butter or margarine. Sprinkle with brown sugar.
Broil bruschetta 4 to 5 inches from the heat for 30 to 60 seconds or until banana slices just begin to glaze. To serve, sprinkle tops with sifted powdered sugar and garnish with chocolate curls, if desired. Serve immediately. Makes 6 bruschetta.