Preheat oven to 350 degrees and coat a 13x9 pan with cooking spray. You may also grease and flour the pan if you would like to remove the cake from the pan before frosting.
Peel and core apples. Chop apples fairly fine (I used a hand chopper that I have from Pampered Chef, I love that thing!!) If you don't have a chopper, a knife will work fine too. Measure apples and set aside.
Begin with dry cake mix in a large bowl, add apple pie spice to dry mix.
Add oil, water, and eggs and beat according to package directions. Usually 2 minutes on medium speed.
Fold in chopped apples.
Pour batter into prepared pan, tap pan firmly on counter to remove any air bubbles.
Bake at 350 for 34 to 38 minutes or until a toothpick inserted near the center comes out clean. Cool pan on a wire rack.
When cake is cool, spread with frosting and serve. Refrigerate any leftovers.