Preheat your oven to 375°F (190°C) and butter a 9-inch baking dish to prevent sticking.
In a large bowl, gently toss the blueberries with granulated sugar, lemon zest, and lemon juice until evenly coated. The berries will start to release their juices, creating a fragrant, syrupy mixture.
Sprinkle the flour over the berry mixture and gently fold it in to thicken the filling slightly. Transfer this mixture into your prepared baking dish, spreading it out evenly.
In a separate bowl, combine the flour, rolled oats, sugar, and cinnamon if using. Add the cold butter cubes and use a pastry cutter or your fingertips to mix until the mixture resembles coarse crumbs with some larger clumps.
Sprinkle the crumbly topping evenly over the blueberry filling, covering it completely for a crisp, golden crust.
Bake in the preheated oven for about 40 minutes, or until the topping is golden brown and the filling is bubbling around the edges. The aroma of baked berries and buttery topping will fill your kitchen.
Remove the cobbler from the oven and let it cool slightly. Serve warm with a scoop of vanilla ice cream or a dollop of whipped cream for a perfect finish.