Bring the oatmeal to a simmer with milk or water. Cook, stirring constantly, until a porridge is formed. As soon as the mixture is thicker, turn the stove down to low and let the porridge steep a little. Add the protein powder and cinnamon. Stir again and the porridge is ready to serve.
Personally, I like to add nuts, berries or other fruit and quark on top. Chia seeds are also very suitable.
The great thing about this recipe is that everyone can modify it as they want.