Preheat the oven to 350°F (175°C). Grease a 9x9 inch baking pan.

In a mixing bowl, combine flour, sugar, melted butter, and salt. Mix until crumbly.

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

In another bowl, combine blueberries, sugar, cornstarch, lemon juice, and vanilla extract. Stir gently to coat the blueberries.

Spread the blueberry mixture over the crust in the baking pan.

In a bowl, mix oats, brown sugar, flour, softened butter, and cinnamon until crumbly.

Sprinkle the oat mixture evenly over the blueberries.

Bake in the preheated oven for 30 minutes, or until the topping is golden brown.

Allow to cool before cutting into bars.