01 - Preheat your oven to 375°F. Lightly grease a 9-inch baking dish with butter or cooking spray.
02 - In a large bowl, combine strawberries, rhubarb, granulated sugar, cornstarch, vanilla extract, and lemon juice. Toss until the fruit is evenly coated with the sugar mixture. Pour the fruit filling into the prepared baking dish and spread evenly.
03 - In a separate bowl, whisk together flour, oats, brown sugar, cinnamon, and salt. Add the cold cubed butter and work it into the dry mixture using your fingertips or a pastry blender until coarse crumbs form. Some pea-sized pieces of butter should remain for texture.
04 - Sprinkle the crumble topping evenly over the fruit mixture, covering the entire surface.
05 - Bake for 35 to 40 minutes until the topping is golden brown and the fruit filling is bubbling around the edges. If the topping browns too quickly, tent loosely with foil.
06 - Let the crumble cool for 10 to 15 minutes to allow the filling to set. Spoon warm portions into bowls and top each serving with a scoop of vanilla ice cream.