Preheat oven to 375F.
Combine first 4 ingredients in a medium bowl. Spoon into an 11 X 7-inch baking dish. Lightly spoon flour into a dry measuring cup, and level with a knife. Combine flour, brown sugar, oats, and cinnamon, and cut in the butter with a pastry blender or 2 knives until the mixture resembles coarse meal. Sprinkle over the blueberry mixture. Bake at 375 for 30 minutes until bubbly. Top with a scoop of ice cream and serve.
Cook's note: Topping may also be made in the food processor. Place flour, brown sugar, oats, and cinnamon in processor, and pulse until combined. Add butter, pulse 4 times or until the mixture resembles course meal.