4 T unsalted butter at room temperature, cut into pieces
3/4 C rolled oats
Preheat oven to 375°F. Grease a shallow 1 1/2-quart baking dish with butter or margarine, or spray with vegetable cooking spray.
Spread the blueberries evenly over the bottom of the prepared baking dish and sprinkle with the lemon juice.
In a bowl, using a pastry blender or fork, mix together the brown sugar, flour, cinnamon, butter and rolled oats until well combined. Sprinkle evenly over the blueberries.
Bake until the top is golden and the blueberries are bubbling, about 30 minutes. Transfer to a wire rack and let cool. Serve hot or warm.
