Preheat the oven to 350 degrees.
Grease an 8x8 square baking pan.
Toss the diced strawberry & rhubarb with sugar and cornstarch. Set aside to sweeten for 10 minutes.
Combine flour, oats, sugar, cinnamon and salt. Add in the cubed cold butter pieces. Work together the topping until it is chunky and crumbly. It should feel damp and all of the flour should be combined.
Spread the crumbly topping all over the top of the fruit.
Bake at 350 for approximately 25-30 minutes or until the topping is golden brown and the fruit is bubbling through.