Preheat oven to 375 degrees. Grease casserole dish or 9 x 9 baking dish with cooking spray.
In a large bowl combine rhubarb, strawberries, sugar, cornstarch and salt. Toss to combine and set aside for five minutes. Pour into prepared baking dish.
In a small bowl, combine rolled oats, brown sugar, melted butter, and cinnamon. Mix until the mixture resembles a coarse crumb.
Spoon oat mixture on top of rhubarb and bake for 40-45 minutes until crisp is lightly browned and bubbly. Serve with a scoop of vanilla ice cream, optional.
Notes
Rhubarb: you can usually find rhubarb at the grocery store when it is in season, April to June. You can also find it at your local farmer's market and sometimes in the frozen fruit section. Just be sure to thaw before using.
Sweetness: adjust the amount of sugar you use depending on the tartness of rhubarb and strawberries you are using.
Leftovers: Refrigerate any uneaten crisp in an airtight container. I like to eat mine the next morning with some nonfat greek yogurt too.
Gluten free: this crisp doesn't contain any gluten. If looking to make the recipe gluten-free, opt for a certified GF oat brand.