Grind the rolled oats to turn them into flour. Mix with the wholemeal flour, brown sugar, powdered cinnamon, bicarbonate of soda and salt.
Mash the bananas with a fork and add to the mixture. Dilute the cornflour in 4 spoonfuls of cold water and add it and the vegetable drink to the mixture. Stir well. Finally, add the crushed walnuts and mix together.
Line a cake mould with baking paper, fill with the cake mixture and bake for about 30 minutes at 170 ºC.
Use a skewer or sharp knife to check whether it is ready: if it comes out dry, the cake is done!