In a large bowl, stir together apple slices, brown sugar, cinnamon and a sprinkle of salt. Spread the mixture into a preferred baking dish sprayed with non stick spray. (I used a 9 x 13 pan).
In a separate bowl, combine cake mix, oats (if using), melted butter and milk. Mix until you have a smooth batter. Spread the cake mixture over the seasoned apples.
Bake at 350 degrees F. for approximately 30-35 minutes, or until the top is golden brown. (If you use a smaller/deeper pan, you may need to increase your time). Serve with preferred vanilla ice cream