Preheat oven to 400°F. Combine blueberry base ingredients - blueberries, sugar, lemon juice and flour. Gently stir.
Pour in the bottom of a lightly greased 9 x 13" baking dish.
Combine flour, brown sugar, rolled oats, cinnamon and salt. Add chopped up butter and put in a food processor. Pulse the food processor in 2-3 second intervals until the mixture is clumpy.
Spread oatmeal mixture evenly over the blueberries. Bake for 20 - 25 minutes until bubbly and lightly golden.