1.Place noodles in a medium heatproof bowl.Cover with boiling water; stand until noodles are tender. Drain.
2.Toast sesame seeds in a wok over high heat, stirring, until golden and fragrant. Remove from wok immediately.
3.Peel and devein prawns, leaving tails intact.
4.Heat half the oil in wok over high heat; stir-fry prawns and scallops, in batches, until prawns change colour. Remove from wok.
5.Heat remaining oil in wok; stir-fry brown onion and carrot until onion begins to soften. Add noodles and sauces; stir-fry 3 minutes. Return prawns and scallops to wok with pak choy and green onion; stir-fry until pak choy just begins to wilt. Serve stir-fry sprinkled with sesame seeds.
When buying prawns, look for brightly coloured, firm prawns with shiny shells and a pleasant fresh sea smell. As prawns are highly perishable when raw, some may be boiled at sea, as soon as they are caught, to preserve them. When cooking prawns, buy green (raw) prawns, as cooked ones will toughen if reheated.