Heat oil in a large saucepan or pot. Add leek, carrot, celery and garlic. Cook over low heat for 5 minutes. Stir in mushrooms and cook a further 5 minutes until mushrooms are tender and softened.
Add stock, water, barley and thyme to pot. Bring to the boil, reduce heat and simmer for 35 minutes until barley is tender. Stir in soy sauce.
Just before serving stir in parsley and season well. Accompany with parmesan toasts.