Add 5 cups water and the broth vegetables to a medium size pot. Bring it to a boil over high heat. Reduce the heat to medium and simmer for about 15 minutes. Discard the vegetables. Season with the soup soy sauce, salt and pepper to taste.
Cut the mushrooms into bite size slices (about 1/4-inch thick). Mushrooms cook down quite a bit, so don’t cut too thin. If using oyster mushrooms, split lengthwise into bite size pieces.
Neatly arrange the mushrooms and scallions in clusters along with other vegetables, if using, in a shallow pot. Add 2 cups of broth. Boil over medium to medium high heat until mushrooms are softened,
4 – 5 minutes.