In a large bowl using an electric mixer, mix together boxed cake mix, water, oil, eggs, baking soda and baking powder on medium speed for 2 minutes. Mixture should be combined and smooth. Add bananas; mix until combined.

Scoop batter into cupcake liners, no more than ⅔ full. Bake for about 13-15 minutes. Check cupcakes around 14 minutes to avoid over-baking. Insert a toothpick into the center of the cupcake, if it comes out clean it is done. Remove cupcakes from oven and allow cupcakes to cool in cupcake pan for 3 minutes; transfer to wire rack and cool completely. Cupcakes should be cooled completely before frosting.

In a large bowl using an electric mixer, cream butter and shortening until creamy and smooth. Add salt and water; mix until combined.

Turn mixer on lowest speed and slowly add 1 lb of powdered sugar; mix until creamy. Scrape down bowl as necessary.

Turn mixer on medium speed for 1 minute. Turn mixer to slowest speed. Slowly add remaining 2 lbs powdered sugar and clear vanilla extract. Blend until creamy.

Turn mixer on high speed and mix for 4 minutes, or until fluffy.