In a large stockpot, bring chicken and broth to a boil. Reduce the heat and simmer until the chicken is tender, about 30 minutes. With a slotted spoon, remove the chicken from pot and, after it cools, shred the meat. Set aside the stockpot of broth.
Place chiles in a medium saucepan, cover with cold water, and bring to a boil. Reduce the heat and simmer until the chiles are soft, about 10 minutes. Drain the chiles and remove the seeds, stems and veins.
Place the chiles, tomatoes, onion, garlic, and salt in a food processor. Process until smooth, adding a 1/2 cup of the reserved broth if mixture is too thick.
Stir the chile puree and half of the cilantro into the broth. Simmer for 20 to 30 minutes. Add salt if needed. Stir in the chicken and the remaining cilantro. Remove the pot from heat.
In a large skillet, heat the oil over medium-high heat. Add a handful or two of tortilla strips, and fry until lightly browned around the edges, about 45 seconds. Transfer the strips to paper towels to drain.
Place a few tortilla strips and a scoop of lettuce in each bowl. Add soup, and top with avocado and a sprinkle of queso. Serve.
Source: Eva's Kitchen and People Magazine 2/21/11