Place hens in a large heavy-duty zip-top plastic bag.
Stir together soy sauce and next 3 ingredients; pour into cavities and over hens. Seal and chill, turning often, 3 to 4 hours.
Bring barley and broth to a boil in a saucepan; cover, reduce heat, and simmer 45 minutes or until liquid is absorbed. Remove from heat; stir in mush-rooms, water chestnuts, and chopped green onions.
Remove hens from marinade, reserving marinade.
Stuff hen cavities with barley mixture, reserving extra mixture. Place hens, breast side up, on a rack in a shallow roasting pan.
Bake at 375° for 1 hour and 30 minutes or until a meat thermometer inserted into stuffing registers 165°, basting occasionally with reserved marinade. Serve with reserved barley mixture. Garnish, if desired.