For the cod with coconut and mushrooms, first cut the cod into rough cubes. Peel the shallots and garlic. Cut shallots into small cubes, garlic into thin slices. Cut lemongrass and chili pepper in half lengthwise.
Heat the wok not too hot, sauté the shallots, garlic and mushrooms and deglaze with the soup. Add lime leaf, lemongrass and halved chili pepper and simmer for about 10 minutes. Add coconut milk and simmer for another 5 minutes. Then season with fish sauce, salt and sugar, remove from heat, add the fish and let simmer for about 10 minutes.
Serve cod with coconut and mushrooms with fresh coriander, lime wedges and chili oil.