Preheat oven to 350 degrees. Line a standard muffin tin with paper liners. Set aside.
In a medium bowl, combine flour, baking powder, baking soda, cinnamon and salt. Whisk together until well combined.
In the bowl of a stand mixer fitted with a paddle attachment, beat butter and sugar until light and fluffy, about 2 minutes. Add eggs one at a time, beating until well blended. Add vanilla and continue to beat for an additional 3 minutes at medium speed, scraping down the bowl as needed. Stir in half the flour and mix until combined, then stir in the buttermilk and then the remaining flour mixture. Do not over mix. Gently fold in the bananas.
Spoon the batter into the liners, filling 2/3 full. Bake for 18 minutes or until toothpick inserted in center comes out clean. Repeat until all batter is done. Allow the cupcakes to cool completely before frosting.
Frost cupcakes with chocolate buttercream. I used a Wilton 2D tip to pipe the rose. Sprinkle with finely chopped walnuts, if desired. Cupcakes will keep in airtight container in refrigerator for 3 days.