Boil chicken breast with 4 cups of water. Add onion, black pepper, bay leaf, garlic head for a flavorful broth.
Shred the chicken and keep aside.
For the Tinga sauce, in a blender, puree tomatoes, chipotle peppers in adobo sauce, and ¼ cup of the stock. In a saucepan with a teaspoon of oil, pour in the puréed sauce.
Add the spices (cumin, chicken bouillon, oregano, black pepper) and simmer the sauce for about 10 mins or longer if you have patience. Add the reserved broth slowly (I add about a cup more).
Add in the shredded chicken and mix well.
To assemble, toast your tostadas, smear refried black beans, top with chicken Tinga, pickled onions, shredded lettuce, radishes, cotija cheese, avocado and cilantro. Drizzle the crema or my Cotija sauce and enjoy.