Preheat the oven to 350 degrees F. Grease a 9"x13" pan and set aside.
In a large bowl, mix together oats, flour, baking powder, baking soda, salt, and cinnamon. Cut in butter with a pastry blender until mixture resembles coarse crumbs.
In a small bowl, mix together milk, lemon juice, and vanilla extract. Stir into oat mixture just until combined.
In a food processor, pulse together the sugar and cornstarch. Add 1 cup of blueberries and pulse until chopped.
Press half of the oat mixture into the bottom of the prepared pan. Spread sugar/berry mixture on top. Top with remaining blueberries, then remaining oat mixture. Sprinkle with turbinado sugar.
Bake in preheated 350 degree F oven 50 to 55 minutes, until light golden brown. Cool completely before cutting into squares.