Combine the blueberries, sugar, vanilla, and cornstarch.
Divide the mixture between two 6- to 8-ounce capacity baking dishes.
To make the topping and assemble:
Combine the flour, oats, brown sugar, cinnamon, and salt. Add the butter, and mix with a fork, a pastry blender or your fingers until the mixture forms crumbs.
Sprinkle the oat mixture over the top of the filling. Placed the baking dishes on a lined, rimmed baking sheet to catch any potential spills.
Bake 15 to 20 minutes, or until the topping has browned and the filling is bubbly.