- Place an oven rack in the middle of the oven. Preheat oven to 375°F.
- In a medium bowl, mix berries, sugar, all-purpose flour and cornstarch.
- Spray a 9 x 9-inch baking dish with nonstick cooking spray. Pour fruit mixture into the baking dish.
- In a medium bowl, combine oats, whole wheat flour, brown sugar, salt, cinnamon and vanilla extract. Mix in butter until crumbly.
- Sprinkle oat mixture evenly over berry mixture.
- Bake until topping is golden brown about 45 minutes. Serve warm or at room temperature.
Thaw the frozen fruit on a plate in the refrigerator overnight or place the frozen berries in cold water for 5-10 minutes and then drain.