Heat 1cm oil in a wok until it is very hot, the oil should look shimmery, and add the noodles. Fry them until they puff up, turning them over to cook them on both sides. You don’t want them to brown, just puff. Drain them on kitchen paper. Wipe the wok out and fry the asparagus spears just long enough to warm them through, tip them onto a serving plate and break over the noodles, scrunching them between your fingers. Spoon over the dressing followed by the remaining herbs. Toss everything together at the table so the noodles remain crunchy.