Heat oven to 375°F. Mash 2 of the bananas to measure 1 cup mashed; reserve remaining 1/2 banana. In large bowl, beat sugar, butter, vanilla, eggs and mashed bananas with electric mixer on medium speed, or mix with spoon, until well blended. Stir in flour, baking powder and salt. Stir in chocolate chips and 1/2 cup walnuts.