Heat the oven to 350 degrees. I like to bake the crisp in a 10 to 12 -inch cast iron skillet but you can also use a 9-by-12-inch baking dish or similar casserole dish. Grease the baking dish lightly with oil spray, if you'd like.
Chop the strawberries and rhubarb into approximately 1/2-inch pieces. Place the fruit into the skillet or baking dish.
Add the sugar, cornstarch, and salt. Toss everything together to combine. I find using my hands works best. Spread the fruit mixture into an even layer.
To a large bowl, add the oats, flour, sugar, maple syrup, salt, and cinnamon. Stir to combine all of the ingredients.
Add the butter then use the tips of your fingers to pinch the butter into the dry ingredients. Keep mixing until a rough, crumbly dough forms.
Crumble the topping over the fruit.
Bake until the fruit is bubbly and the topping is golden brown, about 30 minutes.
Serve warm or room temperature with ice cream or Greek yogurt, if you'd like.