How to Make It
In a saucepan, cook the miso, chicken stock, mirin, vinegar, ginger and garlic over moderate heat, whisking, until hot, 3 minutes. Whisk in the soy sauce and move off the heat.
In a large cast-iron skillet, heat 1 tablespoon of the oil. Season the salmon with salt and piment d'Espelette; add to the skillet and cook over high heat, turning once, until lightly browned, 2 minutes total. Transfer to a plate.
Working in a well-ventilated kitchen, wipe out the skillet and add the hardwood chips. Cook the chips over high heat until they start to smoke, 5 minutes. Place a wire rack over the skillet and set the salmon on it. Tent the salmon with a large sheet of heavy-duty foil and smoke for 5 minutes, until the salmon is medium within. Transfer the salmon to a plate.
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.
Piment d'Espelette, a mildly spicy red pepper, is available at specialty food shops and lepicerie.com.