Make the sauce by stirring all of the sauce ingredients together in a small bowl (coconut aminos, water and soy sauce).
Rinse the shiitake mushrooms and soak them in water for at least 30 minutes (you can use cold or warm water - it doesn’t matter). You can soak them up to an hour.
Cook the soba noodles until soft, but not mushy, about 4 or 5 minutes. Strain the soba in a strainer, rinse with water and set aside.
Heat a large skillet over medium heat for about 2 minutes and then add the onion and cook for 5 minutes, adding a splash of water and stirring each time they start to stick to the skillet. This process will caramelize the onions, releasing their natural flavor and sweetness.
Strain the mushrooms, discard the water and cut the mushrooms in half. Add the mushrooms, carrot, bok choy, and garlic to the skillet and cook for an additional 3 minutes, stirring regularly.
Transfer the cooked and drained soba noodles to the skillet, along with the green onions and the Sauce that you set aside earlier, and cook for an additional minute, gently stirring so that all of the ingredients get incorporated and all of the noodles heat up.
Sprinkle with sesame seeds when serving.