Bring 2 ½ quarts lightly salted water to a boil in a wok over high heat; add in pasta and stir to prevent sticking.
Cook, stirring occasionally, until just tender, for 10-12 minutes; drain well and set aside; dry the wok.
Set the wok over high heat, add in 1 ½ tablespoons oil.
Add the mushrooms and 1 teaspoon salt; stir-fry until tender, for about 2 minutes; transfer to a mixing bowl; set aside.
Return the wok to high heat, and add the remaining 1 tablespoon oil.
Add the garlic and onion; stir-fry for 1 ½ minutes; add the remaining ½ teaspoon salt, rosemary, and crushed red pepper; stir-fry 1 ½ minutes.
Add the vegetable stock and bring to a boil; decrease heat to low and cook for 2 minutes, scraping up the brown bits from the bottom of the wok.
Add mixture to the bowl with the mushrooms.
Return wok to high heat; add in mirin and mustard; stir with a wire whisk to blend; bring to a boil; add the reserved pasta and mushroom mixture; cook, stirring 2 minutes.
Toss in the pine nuts; serve.