Preheat the oven to 350°F. Line 18 standard muffin tins with cupcake liners.
Mash the bananas in a large mixing bowl. Add the cake mix, oil, eggs, and water. Whisk until combined. Divide the batter among the prepared muffin tins and bake for 18-20 minutes or until a toothpick inserted into the center comes out clean. Let cool.
Spread or pipe the frosting on the cupcakes.
Notes
The brand of cake mix used is noted in the recipe. Take note of how many ounces are in the mix so that if you need to substitute another brand, you can adjust the rest of the ingredients accordingly, if needed. The amount of frosting needed will depend on whether you pipe or spread the frosting on your cupcakes.