Preheat oven to 375°F (190°C). Spray a square 8x8-inch baking dish with cooking spray.
In a mixing bowl (or right in the baking dish), add berries, sugar, flour and vanilla. Toss to coat. Bake for 12 minutes, until mixture is hot and bubbly. Meanwhile, make the topping.
Add flour, brown sugar and oats to a medium bowl.
Melt ½ cup butter. Pour butter over flour, brown sugar and oats and stir to combine using a fork. Break up larger chunks into small, course crumbs of oat mixture.
Pour mixture over berries. Bake for 35 minutes until berries are soft and bubbly and the topping is brown and crisp.
Let the crisp cool, then serve with ice cream or whipped cream.