Preheat oven to 350°F. Combine flours, Splenda, cocoa, and baking soda. Add bananas, yogurt, egg whites, vanilla, and 1/2 cup walnuts. Stir. Coat a 9 x 13 cake pan with cooking spray. Pour batter into pan, spreading evenly. Bake about 35 minutes. Cool. Raise oven to 375°F. Toast remaining 1/4 cup walnuts 6 minutes. To make frosting, pour 1/4 cup milk into a medium saucepan over medium heat. Stir in Splenda, cocoa, and cornstarch. Slowly add remaining 3/4 cup milk and bring to a low boil, stirring continuously until thick. Remove from heat and stir in butter and vanilla. Cool and spread over cake. Sprinkle walnuts over cake.
Nutritional analysis per serving: 203 calories, 5.4 g fat (1.3 g saturated fat), 26.1 g carbohydrates, 5.9 g protein, 3.8 g fiber Nutritional analysis provided by Self