Soak the vermicelli in boiling water for 4–5 minutes or until soft. Drain, then shorten the noodles by cutting them. Soak the dried black fungus in boiling water for 4–5 minutes or until soft, then drain. Discard the hard stalks and finely chop.
Heat the oil in a small wok and stir-fry the garlic over a medium heat for 1–2 minutes or until lightly browned. Spoon into a small bowl.
Mix the chicken with the coriander, salt and pepper.
Put the stock, soy sauce and preserved radish in a saucepan and bring to the boil. Lower to medium heat and use a spoon or your wet fingers to shape the chicken mixture into small balls, about 1 cm (½ inch) across. Place them in the stock until you have used up all the mixture, then cook for 3–4 minutes. Add the noodles and black fungus and cook for another 2–3 minutes, stirring frequently. Taste and adjust the seasoning.
Spoon into a serving bowl, garnish with spring onions and coriander, and drizzle with the garlic oil.