Preheat the oven to 350°/180°C or 160°C fan oven, and line a muffin pan with muffin liners. Set aside.
Combine dry ingredients in a bowl (flour, baking powder, baking soda, cinnamon, salt) and set aside.
In a large bowl, whisk together the sugar, egg, mashed banana, melted butter, vanilla.
Add the dry ingredients to the wet ingredients, and stir just until mixed.
Using a large cookie scoop, divide the batter between 12 muffin liners.
Bake for 25-30 minutes or until a toothpick comes out clean from the center of a muffin.
Cool on a cooling rack, serve at room temperature.