In a large pan with straight sides on medium heat add the oil. Add the garlic to the hot oil. Saute until garlic is softened and fragrant and has infused the oil.
Add the mustard greens. Season the greens with salt, and pepper, and saute while tossing to wilt. Once wilted add the chicken stock and stir. Raise heat to a simmer, then lower and cook for about 5 minutes more.