Preheat oven to 350°F. Spray two 10-ounce ramekins with non-stick cooking spray and set aside.
In a medium-sized mixing bowl, toss together the chopped apples, flour, and sugar until all of the apple pieces are coated well. Evenly distribute the apple filling between both ramekins and set aside.
To make the topping:
In a medium-sized mixing bowl (or clean out the bowl you used for the filling and reuse it here too) add the flour, oats, brown sugar, cinnamon, and salt and mix until well combined. Add in the cubed butter and work the mixture together with your hands or a fork until it starts to clump together. Evenly distribute the topping between both ramekins on top of the apple filling.
Bake at 350°F for 20-25 minutes or until the apples are cooked through and the topping is lightly golden brown. Allow to cool for about 5-10 minutes. Serve and enjoy.