Preheat oven to 350° and line two large baking sheets with parchment paper. Slice cookie dough into 1/4” rounds. Spread cookies about 1” apart on baking sheet and bake according to package instructions. Let cool completely.
Pour each color sanding sugar into a separate shallow bowl. Using scissors, cut marshmallows in half diagonally and divide halved marshmallows between bags. Dip the cut marshmallow ends in sugar.
Dye the frosting green with a couple drops of food coloring. Place a small amount of frosting on the center of each cookie and place an M&M in the center. Arrange marshmallows around the M&M to look like flower petals.