Preheat the oven to 350'F
Mix the cornstarch and sugar together in a large bowl. Toss in the prepared fruit. Set aside
In a medium bowl combine the oats, brown sugar, cinnamon and flour.
Cut in the vegan butter until the mixture resembles coarse crumbs.
Press half of the oat mixture into the bottom of a 2qt casserole dish.
Pour the fruit over the crust.
Sprinkle the remaining oat mixture over the fruit and press down slightly.
Bake for 40-50 mins if using fresh fruit. Bake for 50-65 minutes if using frozen. You want the juices to be bubbling throughout, not just at the edges, in order for the starch to thicken the liquid.