Core, peel and thinly slice your apples (a bit thicker makes them a bit firmer, really thin makes it mushier). I peel half of the peels off because I like the taste, up to you if you want all peels off. Put them in a bowl.
Mix together your cinnamon, 3/4 c of flour, 1/2 c. oatmeal, 1 c. brown sugar and your cornstarch. (add raisins and/or walnuts if desired)
Add your apples and fold together until all apples slices are coated well.
Spray the inside of your crockpot with non stick spray, or use a liner.
Pour apple mixture inside. Pour apple juice/cider on top of them.
In another bowl mix together 1/2 c. of flour, 1/2 c. brown sugar, salt, your butter - melted, and remainder of your old fashioned oats 1/4 c.
Sprinkle this mixture on top of the apples in your slow cooker.