In a food processor, crush the Oreo cookies and melted butter until well blended.
Press cookie mixture into an even layer at the bottom of the baking pan until the pan is well covered. Place in refrigerator to harden for a few minutes.
In a standing mixer, mix the mint chocolate chips, powdered sugar, and cream cheese until well blended.
Pour the mint chocolate chip/powdered sugar mixture over the cookie layer in the pan.
Place melted semi-sweet chocolate chips into a ziplock back, cut one corner of the bag, and drizzle the melted chocolate over the minty layer in any pattern you choose.
Place the pan in the refrigerator and chill for about 30 minutes before slicing into small cookie bars.