1Heat oven to 350°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray.
2In large bowl, gently toss apples, berries, sugar, lemon peel and lemon juice. Spread fruit in even layer in baking dish.
3In medium bowl, stir together cake mix and buttermilk until blended. Spoon over fruit mixture and carefully spread in even layer, covering as much of fruit mixture as possible. Dot with butter.
4Bake 28 to 30 minutes or until top is golden brown. Cool 15 minutes. Serve warm cobbler in bowls with whipped topping.