Preheat oven to 350 degrees.
In a mixing bowl, combine oatmeal, flour, brown sugar, baking soda, and salt. Melt the butter and pour it over the oatmeal mixture. Mix until incorporated and crumbly.
Press 2/3 of the mixture into the bottom of a 9×13 pan, reserving the rest for topping.
In a separate bowl, mix the blueberries, granulated sugar, and corn starch until evenly coated. Spread over the crust.
Crumble the remaining oatmeal mixture over the blueberries.
Bake for 20-25 minutes or until golden brown. Let cool completely before cutting.