Heat oven to 350 degrees. Prepare cake batter and bake in 2 - 9 inch round pans as directed on package. Cool cakes in pans for 10 minutes. Invert onto wire racks. Cool completely.
Beat cream cheese and sugar in a large bowl with mixer until blended. Gently stir in cool whip and Oreos.
Place one cake layer on plate and spread with cream cheese mixture. Top with remaining cake layer. Mix frosting ingredients and spread on top of cake. Garnish with Oreos.