In bowl, combine the blackberries, sugar, flour, lemon juice, lemon peel and vanilla. Spoon into a baking dish coated with nonstick cooking spray; set aside.
For topping, in a bowl, combine the flour, baking powder and soda. In another bowl, combine egg whites, yogurt, butter, lemon juice, and vanilla; stir into dry ingredients just until moistened. Drop by tablespoonfuls over blackberry mixture.
Bake at 400 degrees F for 30 minutes or until filling is bubbly and topping is golden. Serve with whipped topping.