Slice the scallops horizontally into 2 or 3 disks about ¼ inch thick. Cut the disks into ¼-inch sticks and the sticks into ¼-inch dice. Put the diced scallops in a nonreactive dish and season well with salt. Cover with ¾ cup lime juice and refrigerate for 2 hours, until the lime juice has “cooked” the scallops. Meanwhile, peel and seed the tomato and cut into ¼-inch dice.

When the scallops are cooked, drain off and discard the lime juice. Add the diced tomato, chopped onion, sliced chilies, chopped cilantro, and remaining ¼ cup lime juice. Marinate, refrigerated, for a couple of hours. To serve, wash and dry the prettiest romaine leaves, make a nest with them, and arrange the ceviche over it. Garnish with slices of avocado, cilantro sprigs, and lime wedges. Serve with tortilla chips.