Preheat the oven to 375F.
Put the strawberries and rhubarb in a medium bowl. In a small bowl, stir together the sugar and flour; sprinkle over the fruit and toss to coat.
Transfer the fruit to a baking dish or 9-inch cast iron skillet, shaking all the excess sugar overtop. In the same bowl or in the bowl of a food processor mix the oats, flour, brown sugar, cinnamon and salt. Cut in the butter with a pastry cutter, fork or your fingers (or pulse in the food processor) until the mixture is well blended and crumbly. Scatter over the fruit, squeezing to create larger clumps as you go.
Bake for 45 minutes or until the fruit is soft and bubbling, and the topping is pale golden and crunchy. Serve warm, with ice cream or whipped cream. Serves 6-8.