Heat the oil in a large pan. Sauté the onion for 2-3 mins., add the garlic and mushrooms, sauté for approx. 10 mins. until all of the liquid has evaporated. Add the thyme and sauté for another 1-2 mins. Add the stock and lentils, bring to the boil, simmer on a medium heat for approx. 35 mins. Add the miso paste, purée the soup using a hand blender. If the soup is too thick, add a little more stock until you achieve the desired consistency.
Serve the soup and garnish with the fried mushrooms and parsley.