Preheat the oven to 375 degrees F. Grease 7 (6 oz) ramekins with cooking spray and place on a large baking sheet. Set aside.

First, make the filling. In a large bowl, combine rhubarb and berries. In a small bowl, combine sugar and orange zest. Rub together with your fingers until fragrant. Add the sugar mixture to the rhubarb and berries. Add the orange juice, vanilla, and cornstarch. Stir gently to combine. Set aside.

In a medium bowl, combine oats, flour, brown sugar, ground cinnamon, salt, and melted butter. Stir until mixture is moistened.

Spoon rhubarb and berry mixture into prepared ramekins, about 3/4 full. Crumble oat topping over the rhubarb and berries evenly. Bake for 25-30 minutes or until topping is browned and rhubarb berry mixture is bubbling. Serve warm or at room temperature with ice cream or whipped cream, if desired.

Note-you can make this crisp in a 9-inch baking dish or deep dish pie plate instead of ramekins. If you are making the recipe gluten-free make sure you use gluten-free oats and flour. If you have fresh berries, you can use them instead of frozen berries.