There are two ways to hallow out the apples:
The more time-consuming way is to keep the bottom of the apple intact, by taking a 6" thin knife go around the edge of the apple, and then slicing it into 4 pieces inside the apple so each piece can be removed.
The easy version:
You can cut the top and bottoms off of the apples, then core them, then run a knife around the edge to remove the remaining apple.
Discard the core.
Dice up the applied pieces
Mix with butter and oatmeal, brown sugar, and cinnamon.
optional: add caramels, cinnamon chips, caramel pieces)
Bake for 20 minutes at 350°.
Serve with whipped cream or ice cream.