Preheat oven to 350.
Line an 8×8 pan with parchment paper, and coat with nonstick spray. Set aside.
Place the blueberries in a medium bowl.
Sprinkle the sugar and cornstarch over the blueberries; toss to coat.
Add lemon juice and stir to combine; set aside.
Combine the flour, brown sugar, cinnamon, baking soda, and salt in a large bowl.
Add cubed butter. Use a pastry blender or two forks, and cut the butter into the mixture until it resembles small peas.
Add oatmeal, stir well to combine.
Press approximately 1-3/4 cups of the mixture into the bottom of the prepared pan.
Spread the blueberries on top of the crust.
Sprinkle remaining crust mixture evenly on top of the blueberries and press lightly.
Bake for 45 minutes uncovered.
Cover with foil and bake for an additional 10-15 minutes or until a knife in the center shows only blueberry juice and no raw dough.
Remove from oven and cool on a baking rack.