Divide the Chex cereal into two separate bowls measuring 2½ cups each.
In a food processor, pulse 8 thin mint cookies until fine.
In 2 separate gallon-size Ziplock bags, add ½ cup powdered sugar into each bag. Divide the crushed thin mints into each bag and set aside.
Melt the mint chocolate chips (or green candy melts) and milk chocolate in separate microwave-safe bowls. Add ½ teaspoon of shortening into each bowl of chocolate. Melt in the microwave, stirring every 30 seconds, until melted.
Once melted, add each bowl of chocolate to one bag of cereal. Stir until the cereal is coated well with the chocolate.
Add the mint chocolate-coated cereal and the milk chocolate-coated cereal separately to each prepared bag of powdered sugar/cookie mixture. Shake until they are coated and enjoy!