In a medium pot, place chicken, water, 2 teaspoons salt, 1 garlic clove and 2 quarters of onion. Cover and simmer about 30 minutes on medium to high heat. Reserve the stock. Allow the chicken to cool, then shred.

In a blender, add the 2 additional quarters of the onion and tomato, chipotle peppers, remaining salt, 1 garlic clove, and enough chicken broth to fill the blender half way, then process until smooth.

Heat the oil in a large deep pan, over medium heat. Once hot, but not smoking, stir in four quarters of one onion and cook until soft and translucent, 5-6 minutes. Add tomato and cook for an additional 10 minutes. Add the cooked chicken, chipotle sauce from blender and more chicken broth, if too dry. Bring to a boil, reduce heat, cover and simmer for 10 minutes. Add salt to taste.

In a heavy skillet, heat 1/4 inch oil. Fry tortillas, one at a time, in hot oil for 20-40 seconds on each side, or until crisp and golden. Drain on paper towels. Keep warm in foil, in a 250 degree oven. Store bought tostadas can also be used.

To assemble, place a warm tostada on a serving plate, spoon on chicken tinga, lettuce, 1-2 slices of ripe avocado, crumbed queso fresco and crema or sour cream. Drizzle with salsa to taste.