Coat a 13x9x2-inch baking pan or 10-inch fluted tube pan with cooking spray. Set aside.
In a large mixing bowl, stir together the cake mix and pudding mix. Add the water, thawed egg product, and applesauce. Beat with an electric mixer on low speed until combined. Beat on medium speed for 2 minutes more.
Spread cake batter in prepared pan. If using a 13x9x2-inch pan, sprinkle chocolate pieces atop cake batter, then sprinkle with walnuts. If using a fluted tube pan, sprinkle walnuts first, then chocolate pieces.
Bake in a 350 degree F oven for 35 to 40 minutes for 13x9x2-inch pan or until a wooden toothpick inserted near center comes out clean. Bake 10-inch tube pan for 45 minutes; toothpick may not come out clean. If using a 13x9x2-inch pan, cool completely on a wire rack. If using a tube pan, cool 10 minutes.
Remove cake from fluted tube pan and cool completely. Serve with whipped dessert topping or non-fat ice cream, if you like. Makes 15 servings.