Bring the chicken stock to a boil in a large saucepan. Stir in the tom yum paste and garlic, and cook for about 2 minutes. Stir in the lemon grass and lime leaves. Place the chicken in the saucepan, and cook 5 minutes, or until no longer pink and juices run clear.

Mix in the mushrooms. Add the fish sauce, lime juice, and green chile pepper. Continue cooking until well blended. Remove from heat, and serve warm with the coriander and basil.