Preheat the oven to 350°F (175°C).
Prepare the blueberry filling: In a baking dish, toss together blueberries, lemon juice, cornstarch, and maple syrup.
Make the crumble topping: In a separate bowl, combine granola and cinnamon (or pumpkin spice mix).
Assemble: Sprinkle the crumble topping evenly over the blueberry mixture.
Bake: Place the baking dish in the preheated oven and bake for 30-35 minutes, or until the topping is golden brown and the filling is bubbly.
Cool and serve: Let the crumble cool for at least 5 minutes before serving. Top with cool whip or whipped cream, if desired.