1. In a medium saucepan, heat the stock to boiling over high heat. Add the barley, reduce heat to a simmer, cover and cook until tender, about 50 minutes. Drain and place in a large bowl.
2. In a medium skillet, heat a few tbs. of stock over medium heat. Add the scallion and celery and cook until the celery is crisp-tender, 5-6 minutes. Add the mushrooms, salt and pepper and cook unitl the vegetables are soft and most of the liquid from the mushrooms has evaporated, about 5 minutes.
3. Stir the cooked vegetables into the barley. Mix well. Serve hot or cold.
5 servings, refrigerates well (makes a great lunch salad).