Core your apples with a knife, making sure to remove all of the core, but the very bottom part.

Mix oats, brown sugar and cinnamon together in a bowl.

Fill each apple with your mixture.  Place them in the slow cooker.

Put a pat of butter on each apple.

If you have any left over topping, spoon it over the top.

Cook on high for 2-3 hours.  Remove from the slow cooker with tongs and serve on a plate.