In a mixing bowl, combine the soy sauce, honey (or maple syrup), rice vinegar, sesame oil, grated ginger, and minced garlic. Whisk until well combined.
Place the salmon fillets in a shallow dish and pour the marinade over them. Cover and marinate in the refrigerator for at least 30 minutes.
Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
Remove the salmon from the marinade and set aside. Pour the marinade into a small saucepan and bring to a boil over medium heat.
In a separate bowl, mix the cornstarch and water until smooth. Add this mixture to the boiling marinade to thicken it. Cook for another 1-2 minutes until it coats the back of a spoon. Remove from heat.
Place the salmon fillets skin-side down on the prepared baking sheet. Brush them generously with the thickened marinade.
Bake in the preheated oven for 12-15 minutes, or until the salmon is cooked through and flakes easily with a fork.
During the last 2 minutes of cooking, switch on the broiler to give the salmon a nice glaze. Keep a close eye to prevent burning.
Once done, remove from the oven and drizzle any remaining marinade over the salmon.
Garnish with sesame seeds and chopped green onions before serving.
Notes
For best results, marinate the salmon for longer if time allows.