Let butter and egg product stand at room temperature for 30 minutes. Meanwhile, line a 9x9x9-inch baking pan with foil. Coat foil with nonstick cooking spray; set aside. In a small bowl, stir together flour, cinnamon, baking powder, and salt; set aside.
Preheat oven to 350°F. In a medium bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add brown sugar and granulated sugar, beating on medium speed until combined and scraping bowl as needed (see Tip). Beat on medium speed for 2 minutes more. Beat in egg and vanilla. Add flour mixture; beat until combined. Stir in pecans and lemon peel.
Arrange the 3 cups apples in prepared pan; spoon pecan mixture over apples and spread evenly (batter will be thick and may not cover all the apple pieces).
Bake 25 to 30 minutes or until a toothpick inserted near the center comes out clean. Cool in pan on a wire rack for 5 minutes. Invert onto a serving platter; carefully remove foil. Serve warm. If using the thin apple slices, cook 12 apple slices in a small amount of boiling water about 1 minute or just until tender; drain well and pat dry with paper towels. If desired, top individual servings of cake with the cooked thin apple slices and/or light whipped dessert topping.
Tip: If using a brown sugar substitute, we recommend Sweet 'N Low® Brown or Sugar Twin® Granulated Brown. Be sure to use package directions to determine product amount equivalent to ½ cup brown sugar. Nutrition Facts per serving with brown sugar substitute: 144 cal., 7 g total fat (2 g sat. fat), 11 mg chol., 120 mg sodium, 18 g carbo., 2 g fiber, 3 g pro. Exchanges: ½ fruit, ½ other carbo., 1½ fat // Carb choices: 1
If the brown sugar substitute is not blending in, let stand for 1 minute and then continue to beat.