In a small bowl, whisk together miso, vinegar, sweetener of choice (honey, maple syrup or brown sugar), soy sauce, garlic and ginger until completely smooth. Set aside.
To prepare the salmon
Liberally mist a baking sheet with oil spray and set aside.
Pat salmon filets dry, then place on the baking sheet skin side down and brush each with about two tablespoons miso sauce. Allow them to marinate for about 30 minutes.
Preheat oven to 425˚ and position a rack to the top spot. Roast salmon in the oven on the top rack for about 10 to 15 minutes.
Set oven to broil and finish under the broiler for a few minutes to crisp the tops, if you’d like them more well done. (A general rule: Cook for about four minutes per 1/2-inch thickness of salmon, or until the internal temperatures reaches 125˚ to 130˚ for medium. Add a few more minutes if you prefer it well done; subtract a few minutes if you want it medium rare.)
Alternatively, you can grill salmon. Make sure fish is at room temperature. Place salmon on a pre-heated indoor or outdoor grill, skin side down. Cook for five to eight minutes, depending on the thickness. Use a wide spatula to carefully flip to the other side and cook for another four to five minutes, or until it reaches your preferred level of doneness. (Note: Salmon should release easily from the grill; if it doesn’t, wait another one minute or two before flipping.) Keep in mind most salmon filets take just about 12 minutes to cook through, so pay close attention to avoid overcooking.
Transfer to a serving dish, brush each filet with additional miso sauce (using a clean brush or fresh spoon) and sprinkle on optional chopped scallions, if desired. Enjoy!