Gather all ingredients.

Soak cedar planks for at least 1 hour in warm water. Soak longer if you have time.

Stir soy sauce, vegetable oil, rice vinegar, sesame oil, green onions, ginger, and garlic together in a shallow dish.

Place salmon fillets in soy mixture and turn to coat. Cover and marinate for at least 15 minutes, or up to 1 hour refrigerated.

Preheat an outdoor grill for medium heat. Place planks on the grill grate. Heat planks until they start to smoke and crackle just a little.

Remove salmon from marinade and place on planks; discard marinade.

Close grill cover. Grill salmon until it flakes easily with a fork, about 20 minutes; salmon will continue to cook after you remove it from the grill.