Preheat oven to 350.
Chop up the Oreos into large pieces.
Prepare the chocolate cake following box directions.
Coat sides and bottom of a 9x13 dish with shortening.
Pour batter into prepared dish.
Bake for 30 minutes or until a toothpick inserted in the middle comes out clean.
Whisk together milk and pudding mix until smooth.
Poke holes all around the top of the cake.
Pour pudding evenly over the cake to allow it to soak into all of the holes.
Sprinkle the top with about half of the chopped Oreos.
Allow to cool completely.
Top with whipped topping and sprinkle with remaining chopped cookies.
Refrigerate for at least 1 hour.