Preheat the oven to 180° C.
Mash 1 banana with a fork and a table spoon of plant based yogurt, until smooth.
In a blender put all of the ingredients except for the cocoa powder.
Blend for 1 minute until smooth and creamy.
At the bottom of the tray place some baking paper (or just use some oil to coat all sides) and pour half of the mixture.
Add the cocoa powder to the remaining half and blend again until combined.
Pour the cocoa mixture on the white one and make some swirls with a fork in order to create the marble effect.
Cut the other banana in 2 lengthwise and place the two halves on the top of the cake.
Bake for 30-45 minutes until after piercing the cake with a skewer it comes out dry.
Enjoy with a sprinkle of icing sugar on top.