Choose you favorite apple slices. I used 3, 21 oz cans of apple slices. Do not use pie filling as it will have syrup/sauce included and you will be adding that later. If you use fresh apples, it will depend of the size of your apples but you will need enough to fill your cake pan.
In a medium sauce pan combine all filling ingredients except vanilla. Slowly bring to a boil, stirring occasionally.
While filling is on stove, work on crust/topping.
Combine flour, oatmeal, and brown sugar in a large bowl. And mix together.
Add cinnamon and melted butter to bowl and mix well. (It works best to use your hands)
At first it may seem that you do not have enough moisture. It may take several minutes to get everything mixed.
Make sure you keep and eye on your filling.
Once your filling is boiling, add vanilla and take off heat.
In a regular cake pan, put a good amount of crust/topping in bottom of pan and press down.
Add apple slices and pour filling over apples. Then sprinkle remaining topping over the top.
Filling may boil over in oven so I like to put my pan on a cookie sheet with parchment paper or foil. It makes for easier clean up.
Bake at 400 degrees for 35-45 minutes. It may be served hot or at room temperature.