Preheat oven to 350°F. Grease three 4-inch cake pans with coconut oil.

Mash the banana in a large bowl. Add the peanut butter, Greek yogurt, coconut oil, and eggs. Stir until well combined and smooth.

Place the oat flour, baking powder, baking soda, and cinnamon in a medium bowl. Stir or whisk to combine.

Add the flour mixture to the banana mixture and mix well.

Divide the batter evenly among the greased cake pans.

Bake for 20-25 minutes, until a toothpick inserted in the center comes out clean. Remove from the oven and let cool completely.

Make the frosting, place the Greek yogurt and peanut butter in a small bowl. Stir until combined and smooth.

Remove the cooled cakes from the pans. If stacking the layers, use a serrated knife to cut and level the tops of the layers.

Spread the frosting on top of each layer. Stack the cakes for a layer cake.

Just before serving, decorate the cake with fresh banana slices if desired.

Store the cake in an airtight container in the refrigerator for up to 4 days.