Preheat oven to 350 degrees (F). Grease/spray your cupcake pan. In a large bowl, mash the bananas with a fork. Next, add all other ingredients but peanut butter and mix until well combined. Once blended, add peanut butter and blend again. Fill each cupcake well to the top. This batter does not rise. Bake the pupcakes for 25 minutes or until a toothpick inserted in the center of one comes out clean. (bake for 15 minutes if using a mini cupcake tin) Allow 3-5 minutes to cool in the pan before removing. Allow pupcakes to cool completely before serving them to your favorite pooch!