Bring a large pot of salted water to boil. When boiling, add noodles, stir, and par-cook them for about 1 minute or until the noodles are slightly pliable. Remove the noodles from the pot and rinse well in cold water; set aside.
In the same pot of boiling water, add spinach, stir, and cook for about 10 seconds. Drain spinach and wash them thoroughly under cold water. Once they are clean, take a handful at a time, and squeeze out all the excess water, then set aside. Season with a pinch of salt.
Heat a large pan (preferably one with deep sloping sides; similar to a wok) over medium-high heat. Add 1 teaspoon of oil and julienned shiitake mushrooms. Sauté mushrooms for about 3-5 minutes. Season with a pinch of salt. Remove from the pan and set aside.
In the same pan, add 1 teaspoon of oil, julienned carrots, and a pinch of salt. Sauté for 1-2 minutes, and set aside.
In the same pan, add 1 teaspoon of oil, julienned red bell peppers, and a pinch of salt. Sauté for 1-2 minutes, and set aside.
Whisk together all the sauce ingredients and add them into the same pan (make sure your pan is large enough to fit all the noodles. If not, you can use a pot for this step).
Bring your sauce up to a boil, then add the par-cooked noodles. Cook the noodles until most of the sauce has been absorbed into the noodles, stirring constantly. Do not overcook the noodles. They should still maintain their chewiness.
Once most of the sauce has been absorbed, turn off the heat, and transfer noodles into a large bowl. Add all the prepared vegetables (spinach, mushrooms, carrots, red bell pepper). Toss to combine everything using tongs and/or your hands.
Garnish with some additional sesame seeds if desired. Serve hot, warm, or at room temperature.