In a large pot, combine the chicken breasts, onion, garlic, bay leaf, and enough water to cover the chicken. Bring to a boil, then reduce heat and simmer for 20-25 minutes, or until the chicken is cooked through. Remove the chicken from the pot and let it cool slightly. Reserve about 1 cup of the cooking liquid.
Once the chicken is cool enough to handle, shred it with two forks.
In a blender or food processor, combine the diced tomatoes, chipotle peppers in adobo sauce, adobo sauce, and chicken broth. Blend until smooth.
Heat the olive oil in a large skillet or pot over medium heat. Add the blended tomato mixture and cook for 10-15 minutes, stirring occasionally, until the sauce has thickened slightly.
Add the shredded chicken to the sauce and stir to coat. Add some of the reserved cooking liquid if the sauce is too thick. Simmer for another 10-15 minutes, allowing the chicken to absorb the flavors of the sauce.
Season with salt and pepper to taste.
Serve the chicken tinga in tacos, tostadas, or over rice. Garnish with your favorite toppings, such as crumbled cheese, cilantro, and sour cream.
