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 until fruit is evenly coated.
03 - Transfer the fruit mixture to a lightly greased 9-inch baking dish, spreading evenly.
04 - In a separate bowl, whisk together flour, oats, brown sugar, cinnamon, and salt. Add cold butter cubes and use fingertips or a pastry blender to rub butter into dry ingredients until coarse crumbs form.
05 - Evenly sprinkle the crumble topping over the fruit mixture, covering completely.
06 - Bake for 35 to 40 minutes until the topping is golden brown and fruit filling is bubbling at the edges.
07 - Let cool for 10 minutes to allow filling to set. Serve warm with generous scoops of vanilla ice cream.