Preheat your oven to 350°F (175°C). This ensures the cake bakes evenly.
Line your baking pan with parchment paper and lightly grease it with coconut oil to prevent sticking.
In a large mixing bowl, mash the ripe bananas until smooth. Add the egg, vanilla extract, and melted coconut oil. Whisk until well combined.
In a separate bowl, combine the cornstarch, baking powder, baking soda, ground cinnamon, ground allspice, and brown sugar. Stir to blend the dry ingredients.
Gradually add the dry mixture to the wet ingredients, stirring gently until just combined. Avoid overmixing.
Fold in the old-fashioned oats and semisweet chocolate chips or nuts, whichever you prefer.
Pour the batter into the prepared baking pan, smoothing the top with a spatula.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes before transferring it to a cooling rack to cool completely.
If you like, mix the powdered sugar with a little almond milk to create a simple glaze. Drizzle it over the cooled cake for a sweet touch.
