Preheat oven to 425 degrees.
Peel apples, cored and then slices into quarters. Then slice each quarter piece into three pieces.
In a large bowl add apple slices, lemon juice, cornstarch, brown sugar, white sugar, vanilla and cinnamon. Gently toss to combine. Pour apple mixture into skillet or 2-quart baking dish and place in preheated oven and bake for 10 minutes.
While apples are baking, in a medium mixing bowl, combine yellow cake mix, brown sugar, salt and baking powder. Stir to combine. Add butter, and using a pastry blender or a fork, cut butter into the mixture until it resembles coarse crumbs.
Add crumb topping to cover the apples entirely. Set in the oven and bake for another 30-35 minutes or until crumb topping is a nice golden brown and the juice from the apples is bubbling.
Serve immediately or let it cool and serve later, it's great either way especially with vanilla ice cream or homemade whipped topping.