In a medium serving bowl, combine all the ingredients. Toss to coat. Cover and refrigerate for 1 hour. (NOTE: When ready, the "cooked" fish should be opaque; if not, marinate slightly longer. Be careful not to leave in too long, as fish will turn mushy.)
Season with salt and freshly ground black pepper, to taste.
Place a lettuce leaf on a plate. Top the leaf with the tortilla nest. Fill with the ceviche and serve.
Yield: 4 to 6 servings