Press into the base of the cake pan and place in the fridge.
The Rest;
Soften both ice creams. You want them slightly melted to the point where you can easily dollop and spread the ice cream over the base.
First spread half of the vanilla ice cream over the oreo base in an even layer.
Spread the cookies and cream ice cream over that in an even layer.
Repeat with the remaining vanilla ice cream and place in the freezer for an hour or two to set.
Slightly crush and break into pieces the Oreos and sprinkle them over the top of the ice cream cake, however you wish.
You can then melt and drizzle over the cookies and cream chocolate and place the cake back in the freezer or wait until you will serve the cake and drizzle just before serving so the chocolate isn't hard.
With or without the chocolate drizzle, place the ice cream cake back in the freezer for at least another two hours to let the ice cream completely set and then serve.