Preheat the oven to 400°F and grease a 9x13-inch metal baking pan.

In a food processor, blend the graham crackers and Oreos for about 30 seconds.

Add the melted butter and blend until it looks like wet sand. Press this mixture into the prepared pan and bake for 10-12 minutes or until the edges are set.

Take it out of the oven and lay Hershey's bars in an even layer on top. Space the marshmallows evenly over the chocolate.

Put the pan back in the oven and bake for another 10 minutes, or until the chocolate is melting and the marshmallows are golden brown.

Let it cool for 3-5 minutes before slicing and serving! These bars are best enjoyed right away, but you can cover and store them at room temperature for up to 3 days.