Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or spray it generously with nonstick cooking spray.
In a large mixing bowl, combine the sugar-free devil's food cake mix, nonfat plain Greek yogurt, and the bottle of Fairlife fat-free chocolate milk.
Mix the batter thoroughly with a whisk or silicone spatula until completely smooth. Ensure you scrape the bottom and sides so no dry pockets of cake mix remain.
Divide the batter evenly among the 12 muffin cups using a cookie scoop, filling each about 3/4 of the way full.
Bake for 18 to 22 minutes, or until a toothpick inserted right into the center of a muffin comes out clean.
Remove from the oven and let them cool in the pan for 5 minutes before transferring the muffins to a wire rack to cool completely.