Preheat the oven to 350ºF. Spray the cups of your muffin pan with a light coating of oil.
Cream together the sugar and butter.
Mash the bananas, and mix in the vanilla, and eggs. Pour this mixture into the creamed mixture and beat to combine.
In a large bowl, whisk together the flour, cocoa, chocolate chips, cinnamon, baking soda, baking powder, and salt. Pour the wet ingredients into the dry, and fold until fully combined.
Spoon 1/2 cup of batter into eight muffin cups. You could also spoon 1/3 cup into all 12 for smaller muffins.
Bake for 20 to 25 minutes. Cool for 5 minutes before removing muffins from pan and serving warm.