Heat oil in a large pot and add the onions, cumin powder, and coriander powder and garam masala. Cook for a few minutes until the onion have softened.
Add the mushrooms and potato and stir to ensure everything is coated in the onion and spices.
Add the vegetable stock, water and coconut milk and bring to the boil. Turn down the heat to a simmer and cook for 15-20 minutes or until the potatoes are completely cooked through.
To finish add soy sauce to taste. Using a stick blender puree soup until smooth and silky.
Optionally, serve with freshly shaved mushroom, sprigs of coriander and a side of naan bread.
