Whisk together soy sauce, brown sugar, garlic, ginger, rice vinegar, and sesame oil in a medium bowl.

Reserve ½ cup; set aside.

Add the salmon filets to a resealable container and pour the remaining marinade over top.

Mix well, seal, and marinate for at least 30 minutes or up to overnight.

Heat grill to 400F.

Grill salmon for 8-12 minutes, flipping once, or until the thickest part of the filet reaches 145F.

Meanwhile, whisk together the cornstarch and water until well-combined.

Add to a small saucepan over medium heat with the remaining ½ cup of marinade.

Bring to a boil over medium-low heat.

Reduce heat to low and simmer for about 5 minutes, or until thickened.

Remove from heat.

Brush teriyaki sauce on salmon after grilling, or serve on the side as a dipping sauce.

Serve topped with sliced green onion and sesame seeds, if desired.