Preheat oven to 350°. Grease 9 x 5-inch baking pan with no-stick cooking spray; set aside.
Whisk egg, brown sugar, bananas, Hellmann's® or Best Foods® Real Mayonnaise and vanilla in large bowl with wire whisk until blended; set aside.
Combine flours, baking powder and salt in medium bowl; stir in 3/4 cup walnuts. Fold into banana mixture just until combined. Turn into prepared pan; smooth top. Sprinkle with remaining 1/4 cup walnuts.
Bake 1 hour or until toothpick inserted in center comes out clean. Cool on wire rack 15 minutes, then remove from pan and cool completely.