In this classic soup, called sopa de lima, from Mexico's Yucatan region, the chicken is not cooked directly in the soup broth because it will make it cloudy. Be careful not to add too much chile or the soup may be too fiery for comfort. You want to maintain a good balance between the tartness of the lime and the heat of the chiles. One large avocado, halved, pitted, peeled and diced, makes a soothing garnish to the spicy broth. Although it's not authentic, 1 cup corn kernels may be added to the soup with the tomatoes.