Lightly spray a 2 quart square baking dish and preheat oven to 375°.

For the Filing: In a bowl stir together blueberries, sugar and flour. Add to baking dish.

For the topping: in a medium bowl combine the oats, brown sugar, flour and cinnamon. With a pastry blender, cut in butter so that it resembles coarse crumbs, then stir in nuts. Sprinkle topping over fruit mixture.

Bake for 30 to 45 minutes or until fruit is tender and topping is golden. If desired serve warm with vanilla ice cream.