Position rack in center of oven and preheat the oven to 375?F. Lightly grease an 11 by 7-inch baking dish with 2 teaspoons of the butter and set aside.
In a medium mixing bowl, combine the strawberries, rhubarb, granulated sugar, cornstarch, and lemon juice. Toss to coat. Pour the strawberry-rhubarb mixture into the prepared baking dish.
In a second medium mixing bowl, add the flour, oats, light brown sugar, and salt, stirring to combine. Add the diced butter to the flour mixture and, using your fingers, work the mixture until it resembles coarse crumbs. Sprinkle the crumb mixture evenly on top of the strawberry mixture.
Place the baking dish in the oven and bake for 40 minutes, until the filling is bubbly and the topping is golden brown.
Using oven mitts or pot holders, remove the crumble from the oven and allow to cool for 10 minutes before serving.
Serve warm with vanilla ice cream, if desired.
Yield: 6 - 8 servings