Coriander sauce is a tart, tangy condiment that can be spooned over grilled kebabs, chops, and chicken. (Cilantro is the Mexican—and by extension American—name for the pungent leaves of the coriander plant.) This version is a permanent fixture on the Afghan table. Similar sauces are found as far east as India and as far west as the Republic of Georgia. Walnuts help thicken and bind the sauce.