Meanwhile, in another large skillet, heat the remaining 2 tablespoons of oil. Add the shiitake and onion and cook over moderately high heat, tossing, until browned in spots and just starting to soften, 4 minutes. Add the fennel and carrots and cook, tossing, until crisp-tender, 2 minutes. Add the turnips and spinach and cook, tossing, until the spinach is just wilted, 1 minute. Season with salt and sprinkle lightly with piment d'Espelette; add 1 tablespoon of the miso dressing and toss well. Transfer to plates. Flake the salmon, scatter it over the salad and serve, passing the remaining dressing at the table.