Preheat oven to 350 degrees. Grease or spray a large bundt cake pan.
Combine cake mix, puddings, oil, water and eggs with electric mixer. Add the peanut butter and mashed bananas and mix until smooth.
Pour batter into cake pan and bake 40 - 45 minutes or until toothpick inserted comes out clean. Once the cake has cooled for at least 10 minutes flip it over and place on a platter or plate. Allow to cool completely before adding the icing.
For the Icing: Combine powdered sugar, softened butter and milk with an electric mixer. Add the peanut butter and mix until fluffy and smooth.
Once the cake is completely cool, ice liberally with the icing and sprinkle with mini chocolate chips if you wish.