Mix oatmeal and protein powder well.
Add unsweetened cocoa powder and stevia, and mix evenly.
Add milk or soy milk to make the dough.
Gently fold in baking powder to the dough.
Lightly grease the baking pan with olive oil.
Pour the dough into the pan and spread it evenly.
Bake in a 180°C oven for 20 minutes.
Let it cool, cut into desired sizes, and serve.