Bake the chocolate cake according to package instructions in a 9x13 inch pan. Let cool slightly.
Using the handle of a wooden spoon, poke holes all over the cake.
In a large bowl, whisk together the instant Oreo pudding and cold milk until slightly thickened.
Pour the pudding evenly over the cake, spreading it into the holes.
Refrigerate the cake for at least 1 hour to set.
Spread the whipped topping evenly over the cake.
Top with crushed Oreo cookies before serving.