Wash the chiles in warm water, carefully slit them open on one side, and remove the seeds and veins.
Bring the white vinegar, red vinegar, and water to a boil in a large saucepan. Add the piloncillo, oil, and salt. Heat until the piloncillo melts. Add the garlic, onions, bay leaves, thyme, peppercorns and allspice. Cook about 8 minutes. Remove from the heat. Add the chiles. Place all of the Chiles Anchos en Escabeche in a covered container and marinate one day at room temperature. They will hold, refrigerated, at least 1 week.
Prepare the Avocado Filling just before serving.
Drain the chiles and stuff with the Avocado Filling. Arrange on a serving platter and drench with the marinade. Decorate with the onion and garlic drained from the marinade. (The chiles may be sliced in half lengthwise and stuffed, for smaller portions.)
Mash the avocados with a fork and stir in the onions, cilantro, chiles, and lime juice. Season to taste with salt and pepper.
c.1997, M.S. Milliken & S. Feniger, all rights reserved