Place chicken, lemongrass, green onion, onion, sliced ginger, chili pepper, peppercorns, and water in a large pot. Cover; bring to boil then simmer one hour.
Add cilantro and mint stems, simmer 15 minutes then strain. Reserve broth and chicken; discard remaining solids.
Shred chicken; discard bones.
Combine chicken, ginger strips, cilantro leaves, sliced mint, soy sauce, and mushrooms in bowl.
Divide broth among bowls; serve with chicken mixture on the side.
Recipe courtesy of University of California Cooperative Extension, Fresno County