Preheat oven to 350 F degrees. Line cupcake pan with liners.
In a medium bowl, mash the banana until no more chunks remain. Whisk in the milk, oil, vanilla, egg and sugar until incorporated.
In a large bowl, whisk together the flour, cocoa powder, baking soda, baking powder, salt and cinnamon.
Make a well in the center of the flour and pour in the wet ingredients. Whisk together just until all the lumps are out.
Fill each cupcake liner 2/3 full.
Bake for 17-19 minutes or until a toothpick comes out clean.
Allow to cool in pans for 2-3 minutes before removing to a wire rack to cool completely.