Put the milk and oat flakes in a saucepan and heat for about 5 minutes, stirring frequently. Add the protein powder and keep stirring. If the porridge becomes too firm, simply add a little more milk or water. Put the porridge in a bowl, if you like, add a pinch of cinnamon.
Heat the frozen berries in the microwave on a low setting or let them thaw beforehand. Cut the banana and add to the pulp with the berries.