Cook decadent double chocolate brownie according to package directions. Let cool, and then crumble into small pieces.
In a medium-sized bowl, combine creamy vanilla shake, Greek yogurt, milk, peppermint extract, and green food coloring, and mix until smooth.
Place one quarter of the brownie crumbles into each of the bottoms of two, pint-sized mason jars. Top each with one-quarter of yogurt mixture. Repeat layers once more. Top with whipped topping, and serve!