Preheat your oven to 375°F.
Grease a 9-inch pie dish or a 2-quart baking dish with butter and set aside.
In a large mixing bowl, combine the blueberries, lemon juice, 2 tablespoons of gluten-free flour, sugar, and salt.
Mix thoroughly to coat the blueberries evenly.
Pour the mixture into the prepared baking dish, spreading it into an even layer.
In a medium mixing bowl, combine gluten-free flour, oats, both sugars, cinnamon, and salt.
Cut in the butter using a pastry blender, fork, or your fingers until the mixture becomes crumbly.
Sprinkle the crumb topping evenly over the blueberry mixture.
Bake in the preheated oven for 25 to 30 minutes, or until the top is lightly browned and the blueberries are bubbling.
Let the crisp cool for 10 minutes before serving.