Preheat oven to 450˚F. Pull mushrooms into thin florets and combine with shallots, then spray or drizzle with oil to coat and season with salt and pepper. Roast 20-25 minutes to crispy, tossing and turning midway.
Heat water to boil (about 4 quarts) for soba and season water with salt once boiling.
Heat a large nonstick skillet or wok over high heat, add oil, 3 turns of the pan, and stir-fry the asparagus 2-3 minutes. Reduce heat a bit and add favas or peas, scallion whites, ginger and garlic, then toss another minute or 2. Add the vinegar or yuzu, mirin or sake, and soy sauce or substitute. Reduce heat to simmer.
Cook soba 1 minute less than package directions. Add soba to sauce and vegetables and wilt in the greens. Drizzle the soba with sesame oil and toss with green onion tops. Serve Soba Primavera in bowls topped with crispy hen of woods mushrooms and shallots, and garnish with sesame seeds.