Preheat oven to 350. Spray 2 9x5 loaf pans with nonstick spray. Cream butter in mixer on medium speed. Gradually add sugar until mixture is fluffy, then add eggs one at a time, beating well.
Beat in banana's on low speed and add 1 cup of flour. Then to the other cup of flour add the cocoa and add to the mix. Add the water/baking soda mixture and then the vanilla just until blended.
Mix in nuts if desired. Spoon batter into loaf pans and bake for 1 hour or until bread test done in the center. Cool bread for an hour then serve or wrap in plastic wrap then a freezer ziplock and put in freezer for up to 2-3 month. So very tasty.