This golden crisp topping is chock-full of oats. Serve with a dollop of plain Greek yogurt, if desired.
Crumble: Preheat oven to 350 degrees. Combine all ingredients in a medium bowl; knead until oil is combined and mixture forms clumps.
Filling: Combine all ingredients in another bowl.
Transfer filling to a 9-inch pie dish. Top evenly with crumble. Bake until bubbling in center and topping is golden, 35 to 40 minutes. Let cool slightly before serving.