Lightly spray a 9x13-inch casserole dish with nonstick spray.
In a medium-sized mixing bowl, combine the crushed Oreos and the melted butter.
Evenly spread and press the cookie crumbs in the bottom of the sprayed casserole dish.
Place in the refrigerator to chill while making the cheesecake layer.
Using a stand mixer, or a handheld mixer and a large mixing bowl, add the softened cream cheese and mix for 1 minute on medium speed.
Reduce the mix speed to low and slowly add the powdered sugar a ½ cup at a time, mixing well after each ½ cup.
Keeping the mixing speed low, slowly add the milk or half-and-half and the mint extract.
Once the milk and mint extract are well incorporated, add the liquid green food coloring one drop at a time.
Using a silicone spatula, be sure to scrape down the sides and the bottom of the mixing bowl. This will keep the color uniform and without streaks.
Remove the cookie crust from the refrigerator and evenly spread the cheesecake layer. Return the casserole dish to the refrigerator.
Using a stand mixer or a handheld mixer and a medium-sized mixing bowl, combine the milk and the instant chocolate pudding mix. Mix on medium speed until the pudding starts to thicken.
Remove the casserole dish from the refrigerator and evenly spread the chocolate pudding over the cheesecake layer.
Evenly sprinkle the mini-chocolate chips over the pudding.
Cover and chill in the refrigerator for at least 2 to 2½ hours.
After chilling, use a offset spatula to evenly spread the container of whipped topping over the pudding layer.
Sprinkle the chopped mint chocolate chunks over the whipped topping.
Notes
To crush your Oreos, you can either do it in a food processor or in a Ziploc bag with a rolling pin.
Make sure your cream cheese is at room temperature so that you don't end up with any lumps in your cream cheese layer.
Chilling this dessert overnight will make it easier to cut and a thicker consistency. If you plan to make it a day ahead, add it to the fridge overnight and then top with the crushed cookies just before serving.