Coat 9x13' dish with non-stick cooking spray.
In a large pan melt butter on medium heat. Add mini marshmallows when butter is nearly melted. Stir frequently.
Add cereal and stir until all ingredients are mixed well.
Pour mixture into dish and coat hands well with water. Keeping fingers wet smooth out the dessert in the dish. Spread remaining 1/2 cup of Oreos on top. Enjoy :)