Preheat the oven to 375°F.
Add blueberries to a large bowl, and add sugar, lemon juice, lemon zest, vanilla, flour, and cornstarch. Toss to combine and transfer mixture to a lightly greased 2qt baking dish.
To another medium bowl, add all the Topping ingredients and combine with a fork until crumbled. Sprinkle the mixture over the blueberries.
Bake for 35-40 minutes or until the top is golden brown and the fruit is bubbly.
Cool slightly and serve warm with ice cream.
