Preheat the oven to 350 degrees F. Grease a 9x13 baking pan with nonstick baking spray.

In a large bowl, add in the blueberries, sugar, cornstarch. Stir until the sugar and cornstarch are combined.

Pour into the prepared baking dish.

In a large bowl, add in the flour, oats, both sugars and cinnamon. Stir until combined.

Add in the butter and coat each slice with the flour mixture to avoid them sticking together. Using a hand mixer, pastry cutter or your clean hands, work the butter into the dry ingredients until the butter is worked in and the mixture is slightly clumpy and crumbly.

Add pieces on top of the blueberry filling making sure to cover most or all of the blueberry filling.

Place in the preheated oven and bake for 40 t0 45 minutes until the topping is slightly golden and the blueberry filling is bubbling.

Let cool to room temperature.

Serve with a scoop of whipped cream or ice cream.

Store covered with plastic wrap in the refrigerator.