Soak shiitake mushrooms in hot water until softened. Squeeze all the water out, then cut into strips and set aside.
Bring a pot of water to a boil.
Blanch the spinach then quickly remove from the boiling water. When cool enough to handle, squeeze all the water out, then cut them into smaller pieces and set aside.
Using the same water, boil the sweet potato starch noodles according to package instructions. Immediately rinse them under cold water, then drain and set aside.
Combine all the sauce ingredients in a small bowl and mix until well combined.
Heat neutral oil in a large nonstick wok or pan over medium high heat, swirling to coat evenly. Add onions and stir for 1-2 minutes.
Add the mushrooms, bell peppers, carrots and scallions and stir for another minute or two, or until cooked to your liking, then add the spinach and give all the ingredients a brief stir.
Add the sauce mixture, immediately followed by the cooked sweet potato starch noodles and mix until coated with the sauce. Serve and top with extra sesame seeds. Enjoy!