Preheat the oven to 350°F (175°C).

In a mixing bowl, combine the blueberries, granulated sugar, lemon juice, and cornstarch. Gently toss to coat the blueberries evenly.

Transfer the blueberry mixture to a baking dish, spreading it evenly.

In another bowl, mix the oats, flour, brown sugar, melted butter, cinnamon, and salt until crumbly.

Sprinkle the oat mixture evenly over the blueberries in the baking dish.

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

Remove from the oven and allow to cool slightly before serving.