Preheat your oven to 350°F (175°C).
Grease and line a small round cake pan (6-inch works well).
In a large bowl, mash the bananas until smooth.
Add the beaten eggs, peanut butter, vanilla, cinnamon, and baking powder.
Mix until well combined.
Fold in the oat flour until a thick batter forms.
Pour the batter into the prepared cake pan and smooth the top.
Bake for 25–30 minutes, or until a toothpick comes out clean.
Let the cake cool completely before frosting.