Cook barley in 1 1/2 cups of stock or water until tender. Add remaining stock or water, tamari, and sherry.
Sauté the onions and garlic in the oil. When they soften add the mushrooms and 1/2 teaspoon salt. When everything is tender add to the barley pot - including any liquid expressed by the vegetables during sautéing. Add black pepper to taste. Simmer, covered, for 20 minutes over the lowest possible heat. Adjust seasonings to taste.