Put the mushrooms in a bowl, cover with water and soak for 20 minutes, then drain and thinly slice.
Combine the curry powder, turmeric and chilli flakes and set aside. In another small bowl, combine the fish sauce and sugar with 2 tablespoons of water. Mix well and set aside.
Heat a wok over medium heat. Add the oil, garlic, diced onion and lemongrass and stir fry until fragrant. Increase the heat to high, then add eel and stir fry for 2 minutes. Add the curry powder mixture and stir fry for 1 minute, then add the vermicelli, wood ear mushrooms, onion wedges and fish sauce mixture. Toss well, then pour in the coconut milk and stir fry for 2 minutes.