Combine the teriyaki sauce ingredients except the corn starch in a small bowl and whisk.
Dry the salmon filets with a paper towel and season with salt, pepper and garlic, gently pressing into the fish.
Add the salmon to a shallow dish or large ziplock bag. Pour half of the teriyaki marinade over the salmon and massage into it. Allow to chill for about 1-2 hours, or up to 8 hours.
Preheat grill to medium-high heat and lightly oil the grate.
Remove the salmon from the salmon from the refrigerator, discard any excess marinade.
Whisk together the corn starch and water until corn starch is dissolved and stir it into the reserved marinade. Transfer to a small sauce pan and heat on medium until thickened. If it becomes too thick, add a splash of water to thin it out.
Place salmon on the grill over direct heat and place skin side up to start, cooking about 6-8 minutes per side, until nice and flakey.
In the last 2 minutes, brush with the teriyaki sauce. Remove from grill, rest for several minutes and serve with an extra drizzle or teriyaki sauce. Serve over rice if desired and garnish with sesame seeds and sliced green onion.