In a medium bowl, mix the finely crushed Oreo cookies with the melted butter until the crumbs are fully moistened. The mixture should resemble wet sand. Press the crumb mixture firmly and evenly into the bottom and up the sides of four to six mini tart pans. Place the crust(s) in the freezer to set while you prepare the filling.

In a large bowl, use an electric mixer to beat the softened cream cheese until it's light and fluffy, with no lumps. Gradually beat in the powdered sugar and cocoa powder until smooth. Add the melted and cooled semi sweet chocolate and the vanilla extract, mixing until everything is well combined and uniform in color.

In a separate, chilled bowl, whip the cold heavy cream with an electric mixer on high speed until stiff peaks form. Stiff peaks mean that when you lift the beaters, the cream holds its shape completely. Be careful not to overbeat, or it will turn into butter.

Gently fold about one third of the whipped cream into the chocolate cream cheese mixture to lighten it up. Then, carefully fold in the remaining whipped cream until just combined. You want to keep the mixture as airy as possible, so use a spatula and gentle, sweeping motions.

Transfer about one third of the filling to a separate bowl. To this smaller portion, add the peppermint extract and a few drops of green food coloring. Stir gently until you achieve a festive shamrock green color.

Remove the chilled crust(s) from the freezer. Spoon the chocolate filling evenly into the crust(s). Then, drop spoonfuls of the green mint filling over the top of the chocolate layer.

Use a toothpick or the tip of a knife to gently drag through the green dollops to create a swirled, shamrock like effect.

Cover the pies with plastic wrap and refrigerate for at least 6 hours, or preferably overnight. This chilling time is crucial for the pies to set properly and for the flavors to meld together beautifully.