Whisk together the miso, mirin, vinegar, soy sauce, scallions, 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.
Preheat a grill to high. Remove the fish from the marinade and season with salt and pepper. Grill the salmon, skin-side down and with the cover closed, until golden brown and a crust has formed, 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.
Fresh lemon or lime juice also work in place of the yuzu juice. Skinless salmon fillets also work well.