Place noodles in a large heatproof bowl, cover with boiling water and leave to stand for 2 minutes, gently using a fork to separate strands. Drain well.
Spray a nonstick wok or frying pan with oil and heat on high. Cook fish in 2 batches for 3 minutes or until browned; set aside.
Reheat wok, add garlic, ginger, lemongrass and onion; stirfry for 2 minutes or until soft. Add bok choy, broccoli and capsicum and stirfry until tender but still crisp.
Combine hoisin sauce, oyster sauce, soy sauce and vinegar; add into wok with fish; reheat. Remove from heat and stir in bean sprouts.
