Preheat oven to 375 degrees. In a large bowl, combine strawberries, rhubarb, sugar, cornstarch, and salt. Transfer to an 8-inch baking dish.
In a medium bowl, combine oats, flour, butter, brown sugar, and salt. Stir until combined and slightly clumpy. Sprinkle over fruit.
Bake until juices are bubbling in the center and topping is golden brown, about 45 minutes. Let cool slightly. Garnish with basil.