Step 1

Combine marinade ingredients in a bowl, add fish and turn to coat. Stand for 10 minutes. Cook the noodles according to packet instructions, then drain.

Step 2

Heat the oil in a wok over high heat. Add drained fish (reserving marinade), and stir-fry for 1 minute. Add onion and capsicum and stir-fry for 2 minutes. Add reserved marinade and simmer for 2-3 minutes until fish is cooked and sauce is slightly thickened. Remove from the heat and fold in watercress, then serve the stir-fry on the noodles.