In a bowl or measuring cup, whisk together soy sauce, sugar, brown sugar, mirin, ginger, garlic and sesame oil. Pour half of the mixture into a Ziploc bag or dish; pour the other half into a small saucepan.
Add the salmon fillets to the Ziploc bag or dish. Toss to coat; marinate for at least 15 minutes or in the refrigerator for up to 2 hours.
Preheat oven to 400 degrees F. Line a rimmed baking sheet with foil and spray with cooking spray.
Remove the salmon from the marinade; place on the prepared baking sheet (skin-side down). Roast salmon in the 400 degree F oven for 8-11 minutes, or until the fish flakes easily with a fork. For an even crispier exterior, place the salmon under the broiler during the final 1-2 minutes of cooking time. Just make sure that you keep a close eye on the fish so that the herbs on top don't burn quickly.
While the salmon is in the oven, prepare the glaze on the stovetop. Heat the reserved marinade in the saucepan and bring to a simmer over medium-low heat. Whisk together cornstarch and water in a small bowl. Add the cornstarch slurry to the saucepan and simmer until thickened. Drizzle the glaze over the salmon just before serving. Garnish with sliced green onions and sesame seeds, if desired.