Vegan Mushroom & Barley Soup

1/4 cup olive oil 1 leek, finely sliced 1 carrot, thinly sliced 1 stick celery, finely sliced 2 cloves garlic, crushed 300g swiss brown mushrooms, thinly sliced 1 litre vegetable stock 2 cups water 3/4 cup, rinsed McKenzie's Australian Pearl Barley 2 sprigs thyme 1 tsp soy sauce 1/2 cup flat leaf parsley leaves, chopped to taste, McKenzie's Australian Natural Sea Salt Large Grinder to taste, McKenzie's Whole Black Peppercorn Large Grinder Parmesan toasts, to serve