Boil a large pan of water for the noodles. Chop the ginger and garlic as small as you can by slicing them very finely in every direction. Cut the spring onions and leeks into thin strips, by cutting the spring onions in half lengthwise and the leeks in halves, quarters then eighths with radial cuts. Cut the strips into 8 cm lengths. Cut the salmon into 2 cm slices.
When you are ready, heat a few tablespoons of oil in the wok over a moderate to high heat and throw the noodles in the boiling water. You now have four minutes! Chuck all the ingredients into the hot oil and stir fry them. Keep moving them around so they don't stick or burn, and turn things over so that all the salmon chunks cook on both sides. The tricky bit is to cook the salmon without it breaking up. Ideally it will be slightly browned in places. I use a big flat spadey thing which came with the wok. When it's cooked, sprinkle lots of soy source all over it, drain the noodles and serve. If there's much fluid in the wok you can drain this off before adding the soy sauce. You need smaller quantities than you might think to make a surprisingly filling, fast and tasty meal.