Preheat the oven to 180°C (356°F).
Mash the banana in a bowl, add eggs, cocoa powder, oat flour, and honey (or stevia), and mix well.
Finely chop walnuts, almonds, or other nuts and add them to the batter.
Pour the batter into a pan lined with parchment paper.
Bake in the oven at 180°C (356°F) for 20-25 minutes.
Let cool, then cut into pieces.