Preheat the oven to 375°F. Spray or butter a 9"x6" inch pan. Set aside.
In a large bowl combine the blueberries, sugar, cornstarch, and lemon juice. Mix to combine.
Place the blueberry mixture into the prepared baking pan. Spread into an even layer. Set aside.
In a medium size bowl add the flour, oats, brown sugar, sat, and cinnamon. Whisk to combine.
Add the cold cubed butter. Using a pastry blender, cut the butter into the mixture until the butter is a tad larger than the size of peas.
Evenly sprinkle the crumble mixture over the blueberries. Bake for 35-40 minutes, or until the crumble is golden brown and the blueberry juices are bubbling.
Remove and let cool for 5-10 minutes. Serve warm with ice cream!