Preheat oven to 375°F. Spray a nonstick loaf pan with cooking spray. In a large bowl, stir together banana, flaxseed, egg whites, agave and buttermilk. In a separate bowl, mix baking soda, salt, flours and orange rind. Combine dry ingredients into banana mixture. Gently fold in blueberries and walnuts. Pour mixture into loaf pan and bake for 45 minutes.