1. Preheat oven to 350F (175C).
2. In a large bowl stir flour, baking powder, baking soda, cinnamon and salt. Set aside.
3. In a separate bowl, mash the bananas, add sugar and stir until combined. Add peanut butter and stir until combined and smooth. Add oil, milk, egg, vanilla and whisk until well combined.
4. Add flour mixture to the wet ingredients and stir until incorporated.
5. Divide between 12 muffin cups. Bake for 15-18 minutes, or until an inserted toothpick comes out clean. Let cool.