Preheat the oven to 350 and coat a large loaf pan with the cooking spray.
Take 2 of the bananas, peel and cut them into small chunks and set it to the side.
Peel and mash the other 3 bananas, and set those to the side.
In a large mixing bowl, sift together both of the flours, baking soda, salt and baking powder and set to the side.
In another large bowl, with an electric mixer, combine the sugar and butter until it is light and fluffy. Then add the egg and mix well.
Alternating ingredients, add the flour mixture, mashed bananas and milk to the butter mixture and mix well. Do not over beat.
Fold in walnuts and banana chunks.
Pour batter into loaf pan and bake for one hour, or until a tester inserted in the middle comes out clean.
Cool for 15 minutes and then transfer to a wire rack to cool completely.
Cut into 18 slices. 1 slice = 1 serving