Preheat the oven to 350 F. In a large bowl, mix together cake mix, eggs, and vegetable oil until smooth.
Use a cookie scoop to place the cookies onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes.
Remove half of the cookies, and set aside. Place one marshmallow and some chocolate chips on each cookie on the baking sheet. Bake for 2-3 minutes. Remove from the oven, and sandwich with the remaining cookies.