01 - Preheat the oven to 350°F.
02 - In a large bowl, combine strawberries, rhubarb, granulated sugar, cornstarch, vanilla extract, and lemon zest. Toss well to coat evenly.
03 - Transfer the fruit mixture to a lightly greased 9-inch baking dish.
04 - In another bowl, mix flour, oats, brown sugar, cinnamon, and salt. Add the cold butter. Using fingertips or a pastry blender, rub the butter into the dry ingredients until coarse crumbs form.
05 - Evenly sprinkle the crumble topping over the fruit mixture.
06 - Bake for 35 to 40 minutes, or until the topping is golden and the fruit is bubbling at the edges.
07 - Let cool for 10 minutes. Serve warm with generous scoops of vanilla ice cream.