Preheat the oven to 350 F. In a large bowl, mix together cake mix, peanut butter, eggs, and vegetable oil until smooth. Fold in the M&Ms. Place the powdered sugar into a shallow dish.
Roll the cookie dough into balls and roll in the powdered sugar. Place the cookies onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes.