Mix the eggs, sugar, flour, vanilla and baking powder to a homogeneous mixture. You can bake as is, just pour it into an oven dish with baking paper in a preheated oven.
But to make it more interesting, set aside a little of the mixture in a cup, add cocoa, 1 more tbsp flour and 1 tbsp milk.
Pour it into a pastry bag and make stripes on the baking paper. Pour the rest of the mixture on top.
Once it's baked, take it out of the oven dish with the baking paper, smear with chocolate spread, add banana slices and wrap into a roll. Leave it in the fridge to harden. You can use other filling of your choice.