1. Preheat oven to 350°F. Spray 13×9-inch pan with nonstick cooking spray.
2. In medium bowl, combine flour, sugar, cocoa, baking soda and salt.
3. In large bowl, combine water, apple sauce, eggs, vinegar and vanilla.
4. Add flour mixture to apple sauce mixture; stir until well blended. Pour batter into prepared pan.
5. Bake 45 minutes or until toothpick inserted in center comes out clean. Cool completely on wire rack.
6. Prepare pudding mix according to package directions using 2 cups skim milk.
7. Spread top of cake with pudding; refrigerate until set. Top evenly with dollops of pie filling; spread over pudding. Cut into 10 pieces. Serve with whipped topping, if desired. Refrigerate leftovers.