In a pot over medium-high heat, heat the vegetable oil.
Saute the sliced shiitake mushrooms until lightly golden brown.
Add the sliced galangal, kaffir lime leaves and lemongrass to the pot.
Add the water to the pot and bring to a boil, then lower the heat to a very gentle simmer.
Add the kombu seaweed and chillies, followed by half the coconut milk.
Add salt, and leave to simmer gently over a very low heat for 10 minutes.
Add the other mushrooms, and cook until softened.
Add the remaining coconut milk, and season with salt to taste if required. Do not boil!
Add the lime juice, and serve once the soup is hot.