Beat the eggs with the sugar until fluffy. To them add the oil and flour with baking powder. Beat well and set aside 3-4 tbsp of the mixture. Pour the greater part into an oven dish laid out with baking paper.
To the set aside part, add the cocoa, stir well and pour the mixture into a pastry bag. Distribute it onto the white mixture, it doesn't have to be even. Bake at 356°F (180 °C) for about 2 min.
Remove from the oven and wrap into a roll using the baking paper.
Stir the mascarpone with the powdered sugar. To it add the whipped cream and stir carefully. Blend 2 of the bananas in a blender with 1 tbsp milk.
Pour the banana puree into the bowl with the cream and mascarpone. Stir well.
Unroll the cooled layer, remove the baking paper and distribute the cream. Arrange the remaining 2 bananas and sprinkle with grated chocolate. Wrap into a tight roll.
Smear it with the whipped cream, pour on the caramel topping, arrange pieces of bananas and sprinkle with grated chocolate.