Preheat your oven to 350°F (175°C).
In a mixing bowl, combine the fresh blueberries, granulated sugar, 2 tablespoons of flour, lemon juice, vanilla extract, and cinnamon. Gently mix to coat the blueberries. Pour this mixture into the baking dish.
In another bowl, mix together 1 ½ cups of flour, oats, brown sugar, melted butter, and salt until crumbly. This will be your topping.
Evenly spread the crumb topping over the blueberry mixture in the baking dish.
Bake in the preheated oven for 35-40 minutes or until the top is golden brown and the blueberries are bubbling.
Remove from the oven and allow to cool for at least 10 minutes before serving.
Serve warm or at room temperature, optionally topped with whipped cream or vanilla ice cream for added indulgence.