1. In medium mixing bowl, stir together first four ingredients. Cut in the 3 tablespoons margarine until crumbly. Set aside for topping.
2. Combine Kellogg's® Complete® Wheat Bran Flakes cereal, flour, baking powder, and salt in medium mixing bowl. Set aside.
3. In large mixing bowl, beat margarine, sugar, egg, and lemon peel until light and fluffy. Add flour mixture alternately with milk, mixing well after each addition. Stir in apples. Spread evenly in greased 9 x 9 x 2-inch baking pan. Sprinkle evenly with cereal topping.
4. Bake at 375°F about 35 minutes or until cake tests done. Cool. Serve with whipped topping, if desired.