Fill a wok or medium saucepan with water, bring to a boil and cook the egg noodles until al dente, about 3 minutes. Drain, then coat with the toasted sesame oil to prevent the noodles from sticking together and set aside.
Heat a wok over high heat and add the vegetable oil. When the wok is smoking, add the garlic and stir-fry until fragrant. Add the mushrooms and cook until starting to brown, 1 to 2 minutes. Season the mushrooms with the Chinese five-spice powder. Stir-fry for 1 minute more, then add the spinach and stir-fry for another minute until wilted (you can add a few tablespoons of water to help create some steam to cook the spinach if necessary). Toss in the cooked egg noodles, season with the light soy sauce and salt. Garnish with sliced scallions, toasted black and white sesame seeds and serve immediately.