This recipe was adapted from Dr. Andrew Weil's book, "The Healthy Kitchen" (Knopf; 2005).
Place walnuts in the bowl of a food processor; process until fine. Add cilantro, jalapeno, salt, vinegar, and 2 tablespoons of water; blend to make a thick sauce, adding in water a tablespoon at a time, if necessary. Taste, and correct seasoning with salt, if necessary. Store refrigerated in an airtight container.