Cook the noodles in boiling water just until al dente. Drain, rinse with cold water, and set aside.
While the noodles cook, in a small bowl, whisk together tamari, mirin, vegetarian oyster sauce, mushroom powder, minced garlic, aonori, sriracha (if using), and cornstarch until smooth. Set the sauce aside.
Heat sesame oil over medium-high heat in a dutch oven or wok. After 90 seconds when the oil is hot, add the shallots, umeboshi plum (if using) and red bell pepper and sauté for 4-5 minutes until softened and fragrant.
Add the shiitake mushrooms, carrots, broccoli, and cabbage. Stir-fry for 4-5 minutes until the vegetables are tender but still have some life in them.
Add the fried tofu, scallions, continuing to sauté for 2-3 minutes until the scallions become fragrant.
Stir in the cooked noodles, and the prepared sauce, tossing everything together to evenly coat. Cook for 3-4 minutes until the sauce caramelizes to the noodles, and everything is heated through.
Serve immediately, garnished with sliced scallions, toasted sesame seeds, nori strips, and pickled ginger, if desired.