Toast chiles lightly, turning constantly so not to burn them. When cool, remove veins and seeds. Cut chiles into small pieces and chop onion and garlic finely. Mix chiles, onion, and garlic with oil, vinegar and salt. Let stand for approx 2 hrs. To serve sprinkle with cheese. (Note: This is sometimes called Salsa de tijera (scissors sauce) since the chiles are usually cut into thin strips with scissors. When chiles pasilla are used the sauce is called Salsa de moscas. Salsa de los reyes has three chiles - mulato, ancho, and pasilla. Good sauce for barbequed meats...)