Preheat the oven to 350°F. In a large bowl, stir together the cake mix, vegetable oil, eggs, and green food coloring until you achieve a dough-like consistency.
Scoop the dough into tablespoon-sized balls. Gently roll the balls between your palms, then roll them in powdered sugar until they are completely coated.
Place the dough balls two inches apart on baking sheets lined with parchment paper.
Bake the cookies for 12-14 minutes or until they are puffed and set. They may look slightly underdone when you first remove them from the oven, which is normal as they will continue to set as they cool.
While the cookies are baking and cooling, craft your fondant hearts in various sizes, if you're not using pre-made heart-shaped candies. Allow the fondant to set and dry before using.
Once the cookies have cooled, dust them with an additional layer of powdered sugar through a fine mesh sieve for a snowy effect.
Use a small dab of icing gel on the back of each fondant heart or candy and press it gently onto the top of each cookie to adhere.