Preheat oven to 350 F. Line an 9×9″ cake pan with parchment paper.
In a blender combine bananas, eggs, maple syrup and vanilla. Blend until smooth.
Scrape down the sides with a spatula then add the dry ingredients: almond flour, oat flour, cornstarch, baking soda, baking powder, salt, cinnamon and nutmeg. Pulse until just combined.
Pour the batter into the prepared baking dish.
Bake for 30-35 minutes, or until the cake is golden brown and a toothpick inserted in the center comes out clean. Cool on a rack.
For the icing: In a medium-sized mixing bowl use a whisk to combine butter, icing sugar, lemon zest, lemon juice and whipping cream.
Pour glaze over cooled cake and using an offset spatula spread across the top of the cake evenly.
Place the cake in the refrigerator to allow the glaze to set.
Slice the cake into 12 slices and enjoy!