In a large bowl, mix together oats, flour, brown sugar, salt, cinnamon, and cold butter cubes with your hands to create a crumbly topping. Set aside.
Make the filling
In a small bowl, mix together cornstarch and brown sugar. Set aside.
In a 10-inch cast iron skillet (or other oven-safe skillet) over medium-high heat, sauté apples until tender, about 5 minutes. Add cornstarch brown sugar mixture, sprinkle cinnamon, and stir to coat.
Remove from heat and add the orange juice. Then top with the topping and bake at 350°F for about 30-35 minutes. The crisp will be slightly bubbling and the top will be golden brown.
Cool on a cooling rack for 10-15 minutes before serving.
Notes
While this is best enjoyed immediately, leftovers will keep in an airtight container in the refrigerator for up to one week.