1. Rinse chilies and cut in half lengthwise. Place 2 chili halves, broth, and lime peel in a 3- to 4-quart pan over high heat; bring to a boil, cover, reduce heat to low, and simmer 5 minutes. Taste broth and, if desired, add more chili and simmer, covered, 5 minutes longer.
2. Meanwhile, pit and peel avocado. Cut lengthwise into thin slices or into 1/2-inch cubes. Arrange equal portions of avocado and tomatoes in each of 4 wide, shallow bowls.
3. With a slotted spoon, lift chili and lime peel from broth and discard. Stir lime juice into broth. Gently ladle broth around avocado and tomatoes in bowls. Sprinkle with cilantro leaves. Add salt to taste.