Preheat oven to 350 degrees F. Lightly coat with cooking spray the bottom only of a 9 by 13 inch glass cake pan.
FOR CAKE: Set grated zucchini in a mesh strainer over a bowl and lightly press with a spatula to release water. In a large mixing bowl, combine the cake mix, cinnamon, eggs, egg whites, nonfat yogurt, and applesauce. Beat on low speed with an electric mixer for 2 minutes, scraping the sides of the bowl often. Fold in drained grated zucchini. Pour into prepared cake pan.
Bake for 45 to 50 minutes or until toothpick inserted into the center of the cake comes out clean. Cool completely. When cool, invert cake onto a large plate or platter, and cut cake into 12 large squares with a clean, sharp knife.
FOR MOUSSE TOPPING: While cake is baking, combine tofu, pudding mix and cinnamon in a bowl. Using an electric mixer beat on high speed for 2 minutes. Fold in the whipped topping with electric mixer on low speed. Cover and refrigerate until ready to serve.
To serve, cut each cake square in half diagonally to make 2 triangles. Use a spoon to decorate each plate with chocolate sauce, set 2 cake triangles on each plate, sprinkle generously with confectioners' sugar and cocoa powder, and dollop with chocolate mousse.