Place salmon fillets in a shallow, nonreactive dish/pan. In a small bowl, whisk together wine, orange juice and soy sauce. Pour over salmon, cover tightly with plastic wrap and refrigerate 2 hours, turning several times.
Preheat oven to 400º. Transfer salmon to foil-lined, rimmed baking sheet, sprinkle with a little salt, and roast for 12 minutes, until just cooked through and easily flaked with a fork. Let rest, loosely tented with foil, for 5 minutes.
Meanwhile, make sauce; place spinach, arugula, mustard, sour cream, half-and-half and garlic in bowl of food processor. Process/pulse for 30 seconds or longer until greens and garlic are finely chopped and blended with other ingredients.
Plate salmon and top each serving with a dollop of mustard sauce, passing any extra sauce in a small bowl.