In a larger mixing bowl, mix the ingredients for the cake batter. Set aside.
In a small mixing bowl, mix the ingredients for the apple mixture. Set aside.
In a small mixing bowl, mix the ingredients for the topping. Cut the butter in with a fork until the mixture is mixed.
Using a casserole slow cooker or a 6 qt slow cooker, spray the inside of the crock with cooking oil.
Pour the cake batter on the bottom of the slow cooker.
Add the apple mixture evenly on top of the cake batter.
Add the topping as evenly as possible to the top of the apples.
Cover and cook on HIGH for 2 hours or until the middle has set and the sides are golden brown.
Remove the crock from the heating element.
Allow to cool and serve slightly warm.