Preheat oven to 350 degrees. Lightly grease cookie sheet. In a medium mixing bowl beat the butter or margarine for about 1 minute. Add the sugar, brown sugar, baking powder and salt, beat until combined. Add the egg, bananas, vanilla, and flour and mix well. Stir in the chocolate chips and nuts. Drop dough by rounded teaspoons 2 inches apart on the cookie sheet. Bake for 25 minutes or until golden. Cool on a wire rack.