Soak the black fungus in a bowl with plenty of boiling water for 20 minutes.
Give the chicken a rinse under a tap, and prepare the soup vegetables.
Put the chicken breast-side down in a large stock pot. Add the water and the rest of the soup ingredients, except the fish sauce and chicken bouillon powder (if using). Turn the heat to high and allow it to come to the boil.
Once boiling, turn the heat down to medium-low. Continue to simmer for 45 minutes, partially covered. Use a spoon to scoop off any scum build up on the surface of the soup.
Drain the black fungus. In a small saucepan, cook the black fungus in fresh boiling water for 5 minutes. Strain and leave aside until assembly.
After 45 minutes, turn off the heat. Let the pot sit with the lid on for 10 minutes.
After 10 minutes, remove the chicken from the pot and check if the chicken is cooked. If not, pop it back into the pot and cook until done. If yes, then let the chicken rest on a plate. Once it is cool enough to handle shred the meat.
Add the fish sauce to the soup and check the seasoning. Adjust according to your taste. Add the chicken bouillon powder if you think the soup needs more flavour.
Keep the soup pot hot on a medium-low heat setting.