1.Soak noodles in boiling water in a heatproof bowl 5 minutes. Stir to separate strands; drain.
2.Meanwhile, place cornflour in a shallow bowl; season. Add fish pieces to coat, shaking off excess.
3.Heat a wok or frying pan over moderately high heat. Add oil; swirl to coat surface.
4.Stir-fry fish, in 2 batches, 4 minutes each batch, or until browned and cooked. Using a slotted spoon, transfer to a paper towel-lined heatproof plate.
5.Reheat wok over moderately high heat. Add ginger and red onion; stir-fry 3 minutes, or until starting to brown. Add vegetables; stir-fry 2 minutes, or until heated.
6.Return fish to wok with sauces and noodles; stir-fry 2 minutes, or until heated.
7.Serve topped with green onion and extra sweet chilli sauce.