Preheat oven to 375℉.
In a bowl, mix together blueberries, cornstarch, granulated sugar, and lemon juice. Toss together until berries are coated.
In a separate bowl, mix flour, old-fashioned oatmeal, brown sugar, cinnamon, nutmeg, and butter. Mix together with a fork until it gets crumbly.
In a 9 x 9 baking dish, add the blueberry mixture in an even layer. Then, sprinkle the crisp mixture in an even layer on top.
Bake for 40 minutes. After baking, the blueberries will be very hot, so make sure to let it cool off for just a few minutes. Serve with whipped cream or a scoop of vanilla ice cream.