Set aside 1/3 of the mixture. Pour the rest of it into an oiled tray covered with baking paper.
To the part you set aside, add the cocoa and stir well. Pour 1/2 the cocoa mixture in a circle over the other one.
Place the peeled bananas on top after rolling them in a little flour. Pour the rest of the cocoa over the bananas.
Bake in a preheated 356°F (180 °C) oven until ready. Take it out and sprinkle with powdered sugar.