Chicken Soup with Ginger and Cilantro

Combine chicken pieces, broth, cilantro stems, scallions, ginger, and salt in a large saucepan; bring to a simmer over medium-high. Reduce heat to medium to maintain a gentle simmer. Simmer, undisturbed, until chicken is cooked through and is easily shredded, 30 to 40 minutes. Transfer chicken pieces to a plate. Let chicken stand until cool enough to handle, about 5 minutes, then shred into bite-size pieces; set aside. While chicken is cooling, increase heat under pan to medium-high, and bring broth mixture to a boil. Boil, undisturbed, until liquid has reduced by one-third, about 15 minutes. Remove from heat. Let cool slightly, about 3 minutes. Pour through a fine wire-mesh strainer into a large heatproof bowl; discard solids.

Wipe pan clean; return strained broth mixture to pan. Bring to a simmer over medium. Stir in zucchini and bell pepper; cook, undisturbed, until vegetables are tender, about 6 minutes. Stir in tomato and shredded chicken; cook, undisturbed, until warmed through, about 2 minutes. Season soup to taste with soy sauce or fish sauce and additional salt as desired. 

Arrange mixed herbs, jalapeños, red onion, and citrus wedges on a platter. Divide hot soup evenly among 6 bowls, and serve alongside aromatic garnishes.