In a medium bowl, combine soy sauce, rice vinegar and sesame oil. Add bok choy, carrots and turnips; and toss to combine. Let slaw sit for about 10 minutes so bok choy can soften.
Pat salmon dry. Lightly season it on all sides with sea salt. Place fillets, skin side down, in a not preheated skillet, preferably cast iron. Cook salmon over medium heat, undisturbed for 5 minutes.
With a spatula, press lightly on the flesh to ensure all parts of the skin are making contact with the pan. Continue to cook, skin side down, until fish is mostly opaque and skin is crispy, about 5 minutes longer. If skin sticks to the pan, don't try to un-stick it—it will be ready to flip when the skin becomes crispy and will release on its own.
Gently flip the fillets and remove pan from heat. Let fish sit in pan and continue to cook, off-heat, for about 1 minute, until it just cooked through.
Divide the slaw between two plates and top with salmon. Drizzle any juices from the slaw over salmon. Garnish with scallions and sesame seeds, if desired; and serve.