In a small jar or bowl, create a sauce for the noodles by stirring the sesame oil, soy sauce, minced garlic, toasted sesame seeds, ground black pepper, and the optional sugar to combine well then set aside.
In a large pot, boil 2-3 litres of water on high heat, then boil the noodles according to the packet instructions until translucent and soft; around 5 minutes.
Use a fine mesh strainer to drain the noodles, rinse them under cold running water, then drain them again, and transfer them to a large bowl. Pour in half the sauce, and stir it in well so the noodles are completely covered. Note: as the noodles soak up the sauce and cool they may lose their transparency.
In a flat-bottomed wok on high heat, heat half a tablespoon of neutral cooking oil until shimmering, then stir-fry the carrot matchsticks for a couple of minutes, then use a slotted spoon to transfer them to a large bowl; using the same oil, stir-fry the onions until soft and translucent, then transfer them to the bowl.
To the same wok, heat a tablespoon of neutral cooking oil and stir-fry the shiitake mushrooms, seasoned with salt, until they start to soften, add the spring onions/scallions and continue to stir-fry until the mushrooms just begin to brown, then transfer to the bowl; and lastly, quickly stir-fry the spinach until soft, and transfer to the same bowl.
Wipe out the wok with a paper kitchen towel, add half a tablespoon of cooking oil, heat until shimmering, return the mixed vegetables and noodles to the wok, add the rest of the sauce, and stir fry for a few minutes, combing everything well until warm again and the noodles are translucent once more.
Transfer to bowls, sprinkle on some more sesame seeds, and serve immediately.