Combine first 5 ingredients in a large bowl; beat with an electric mixer on medium speed until well blended.
In a separate bowl, combine the flour, baking powder, baking soda, and salt. Add the flour mixture to the banana mixture. Add the nuts and stir just until moistened.
Spoon the batter into the prepared pan. Sprinkle the top with sugar and more chopped nuts if you like.
Cool for 10 minutes in the pan on a wire rack. Then remove from the pan and cool completely on a wire rack.