Pre-heat your oven to 425 and prepare a 12 count muffin pan. You can either spray with non-stick spray or use muffin liners.
In a small bowl, mix together the dry ingredients: flour, baking powder, baking soda, and cinnamon.
In a larger bowl, mash the bananas then whisk in the egg, brown sugar, melted butter, milk, and vanilla extract.
Add the dry ingredients to the large bowl with the wet ingredients and stir to combine.
Evenly fill the muffin pans. You should have just enough to make 12 muffins, filled a little over half way each.
To make the cinnamon topping, combine all ingredients in a small bowl and mash together with a fork until the mixture resembles wet sand.
Sprinkle the tops of each muffin with the cinnamon sugar mixture.
Place in the oven and immediately lower the temperature to 350 degrees and bake for 22-25 minutes.