Preheat the oven to 350°F (175°C).
Combine fresh blueberries, lemon juice, granulated sugar, and cornstarch in a mixing bowl.
Transfer the blueberry mixture into a greased baking dish.
Mix oats, flour, brown sugar, melted butter, cinnamon, and salt in another bowl until crumbly.
Sprinkle the topping generously over the blueberries in the baking dish.
Bake in the preheated oven for 30-35 minutes, or until the topping is golden brown and the blueberries are bubbly.
Remove from the oven and let cool slightly before serving.