Bring water to a boil and salt it. Cook the spaghetti to al dente.
While the pasta cooks, heat a large nonstick skillet with vegetable oil over high heat until the oil ripples. Add the chicken and stir fry until golden, 3-4 minutes. Add the garlic, ginger, shiitake mushrooms, scallions and cabbage and stir fry for 2-3 minutes more. Season the stir fry with salt and lots of black pepper and turn off heat.
Place the Tamari (eyeball it) and sesame oil in a bowl and add the hot pasta to the dish. Toss to coat, then sprinkle with sesame seeds. Place pasta in shallow bowl and top with stir fry.