Preheat the oven to 350 degrees. Line 2 large baking sheets with parchment paper. Set aside.
In a large bowl, combine the cake mix, oil, vanilla and eggs. Stir until a dough forms. Fold in mint chocolate chips.
Place dough in the refrigerator for 30 minutes {do not skip this step!}.
Remove dough from the refrigerator and scoop into 1-inch balls. Roll in sugar and place on prepared baking sheets about 1 inch apart.
Bake at 350 degrees for 8-10 minutes. Cool on baking sheet for one minute and then transfer to nonstick cooling rack to cool completely.
In a small bowl, combine 1 cup powdered sugar with 2 Tbsp milk and 1/4 tsp peppermint extract. Stir well until combined.
If needed, add additional milk to reach desired consistency. Drizzle over cookies and sprinkle with crushed candy cane pieces. Let sit for 15 minutes for glaze to set.