Preheat the oven to 350°F and line a 9x13 inch baking pan with parchment paper. In a large bowl, mix the flour, oats, brown sugar, granulated sugar, baking powder, salt and cinnamon.
Stir in the melted butter and vanilla until crumbly.
Press two-thirds of the oat mixture firmly into the bottom of the prepared pan. Reserve the remaining third of the crumb mixture for later.
In a separate bowl, toss the blueberries, sugar, lemon juice, lemon zest, cornstarch, and salt until evenly coated.
Spread the blueberry mixture over the bottom crust.
Sprinkle the remaining oat mixture evenly over the blueberries.
Bake for 40-45 minutes, or until the topping is golden brown and the blueberry filling is bubbling.
Cool completely in the pan. Refrigerate for 1 hour before slicing for the cleanest bars. Cut into squares and serve.