I typed 'banana bread, three bananas' into Google last Tuesday evening, and this Food Network recipe popped up. Although it didn't list any additions like walnuts or chocolate, I figured I would give this one a try and add them on my own.
You can find the recipe from Food Network here. As mentioned above, I added chocolate and walnuts, but I didn't really measure them out. I'm guessing it was about 1/3 cup of each, but this loaf seems pretty forgiving, no matter how many 'extras' you wish to add.