Soak bean sprouts in plenty of water. When crisp, thoroughly drain in a sieve.
Chop the roots of nira (Chinese chives), and cut into 4 cm(1.5 inch) strips.
Cut negi (Japanese long white leek) into half. Chop diagonally into thin slices.
Cut thin pork slices into 2 cm(0.75 inch) pieces.
Heat sesame oil in a Chinese pan over high heat. Stir-fry pork and leek. When the color of the pork changes, add bean sprouts, and stir-fry together with salt and pepper. When all the ingredients are coated with oil, add broth, and stir-fry noodles while loosening the strips.
When the noodles are cooked, add nira, oyster sauce, yakisoba (fried-noodle) sauce, and if you like, some Chinese chili oil, and stir-fry together evenly coating everything with the sauce.
Transfer to serving dishes and sprinkle bonito flakes, green-seaweed flakes, red pickled ginger as you like.
If you like soy sauce, use combination of oyster sauce and soy sauce. If you like hot and spicy flavor, use Doubanjiang (Chinese chili bean sauce) instead of Chinese chili oil for very hot and spicy fried noodles. You may also enjoy wrapping hot spicy fried noodles in a thin layer of omelette dressed with mayonnaise. It goes well with beer!