1. Whisk onions, soy sauce, vinegar, honey and ginger in a small bowl until the honey is dissolved. Place salmon in a plastic Ziplock bag. Place 3 Tablespoons of the mixture into the bag with the salmon and put it in the refrigerator to marinade for at least 15 minutes (a couple of hours is much better).
2. Preheat broiler. Line a small pan with foil. Then spray foil well with non-stick cooking spray.
3. Place salmon into the pan and broil it for 6 to 10 minutes until it is cooked through. Drizzle with the reserved sauce and garnish with sesame seeds.