Combine all the sauce ingredients in a medium bowl and stir until brown sugar is dissolved.
Place salmon fillets in a deep baking dish, or a big bowl. Pour the sauce over the salmon, cover with plastic wrap, and let marinate in the refrigerator for 15 - 20 minutes.
Preheat oven to 400˚F. Line a big baking sheet with foil for easy clean up later.
Transfer salmon fillets to the prepared baking sheet. Reserve the marinade.
Bake for 12-15 min or until salmon is flaky and cooked through. Bake times may vary depending on the thickness of salmon. You'll know when the salmon is done when easily flaked: check the doneness of your salmon with a fork. When the salmon flakes easily with a fork, it's ready, or when it reaches 145º F internally.
While salmon is baking, place the remaining marinade to a small saucepan and bring to a boil then reduce heat to low and simmer, stirring occasionally, until slightly thickened, about 5-8 minutes. NOTE: If you want to thick the sauce even more mix 1 teaspoon of water + 1 teaspoon of cornstarch and add it to the sauce. Remove from heat and reserve to serve with the salmon.
When the salmon is done, remove from oven and brush each fillet with more sauce. Sprinkle with green onions and sesame seed, if desired. Serve with rice and steam veggies.