Whisk together the miso, mirin, vinegar, soy sauce, green onions, ginger, and sesame oil in a small bowl. Place the salmon in a baking dish, pour the marinade over, and turn to coat. Cover and marinate for 30 minutes in the refrigerator.
Heat grill to high. Remove the fish from the marinade and season with salt and pepper. Grill the salmon, skin side down, with the cover closed, until golden brown and a crust has formed, about 3 to 4 minutes. Turn the salmon over and continue grilling for 3 to 4 minutes for medium doneness. Drizzle with a little yuzu juice, if desired, and serve.
Recipe courtesy Bobby Flay