Preheat oven to 350 degrees. Coat a 9x13 baking dish with nonstick cooking spray.
FILLING: Place sliced apples and blackberries in a large bowl. In a small bowl, combine sugar and cinnamon. Sprinkle cinnamon-sugar over the blackberries and apples, gently toss to coat. Pour into prepared baking dish.
TOPPING: In a large bowl, stir together all ingredients until well combined. (I like to use my hands for mixing.) Crumble over fruit.
Bake for 45 minutes or until top is golden brown. Serve warm or cold, topped with vanilla ice cream.