Preheat the oven to 180°C (356°F).
Mash the banana.
In a bowl, mix together the mashed banana, protein powder, eggs, oatmeal, and plant-based milk.
Add baking powder and a pinch of salt, then mix well.
Pour the batter into a pound cake pan.
Bake in the oven at 180°C (356°F) for 30-35 minutes.
Allow to cool completely, then cut into serving-sized pieces.