Bring first 7 ingredients to a boil in a 6-quart Dutch oven. Add fish, reduce heat, and simmer 3 minutes. Drain well, reserving fish but discarding onion, garlic, bay leaf, and cilantro. Flake fish, and set aside.
Heat olive oil in a large skillet over medium-high heat. Add pressed garlic cloves, and sauté 30 seconds. Add tomatoes, 1 or 2 chopped chipotle chiles, cloves, black pepper, and 1 tablespoon lime juice. Bring to a boil, reduce heat, and simmer 10 minutes or until liquid almost evaporates. Process tomato mixture in a blender until smooth; return to skillet. Add fish to tomato mixture, and cook 1 minute or until thoroughly heated. Remove from heat, cover, and keep warm.
Stir remaining chipotle chile into mayonnaise. Stir in 2 teaspoons adobo sauce until blended.
Heat vegetable oil in a 9-inch skillet over medium-high heat. Fry tortillas, one at a time, in hot oil 1 minute or until richly browned and crisp, turning once or twice. Drain on paper towels.
Spread chipotle mayonnaise evenly on tortillas. Top each tortilla with 1/3 cup fish mixture, 1/2 cup lettuce, and avocado slices. Garnish, if desired.
Note: Try this recipe with rotisserie chicken in place of the fish for a quick weeknight dinner.