Preheat the oven to 350°F (175°C). Grease a baking pan.

In a mixing bowl, combine flour, oats, brown sugar, granulated sugar, baking powder, and salt.

Add melted butter and vanilla extract, mixing until crumbly.

Press half of the mixture into the bottom of the prepared baking pan.

In another bowl, mix blueberries, lemon juice, cornstarch, and granulated sugar.

Spread the blueberry mixture evenly over the base in the baking pan.

Sprinkle the remaining crumb mixture on top of the blueberries.

Bake in the preheated oven for 25-30 minutes or until golden brown.

Allow to cool before cutting into bars.