Preheat the oven to 375°F. Spray a round or oblong 2-quart baking dish with cooking spray. Set aside.
In a medium size mixing bowl, toss the blueberries with the sugar, cornstarch and lemon juice. Pour evenly into the bottom of the baking dish.
In a separate bowl mix together the oats, flour, brown sugar, granulated sugar, cinnamon, nutmeg and salt.
Using a pastry blender or 2 forks cut the butter into the dry ingredients until it resembles coarse crumbs. Mix in the nuts until evenly distributed. Sprinkle the topping over the blueberries.
Bake for 40-45 minutes or until golden and the edges are bubbly. Check at 30 minutes and cover loosely with a piece of foil to prevent over browning, if needed.
Serve warm with vanilla ice cream or at room temperature with fresh whipped cream.