Add the chopped tomatoes, chipotle, and chicken broth in a blender. Blend until smooth.
In a large stockpot, add the chicken, water, onion, garlic clove, bay leaf, salt and pepper, and cook until the chicken is no longer pink. Shred it.
Heat oil. Add the onions and caramelize, add the shredded chicken and chipotle tomato sauce. Stir to combine.
Smear refried beans to a tostada. Add tinga, shredded lettuce, sour cream, and cotija. Enjoy!