Soak the cedar planks for at least 1 hour in warm water. Soak longer if you have time.
In a shallow dish, stir together the vegetable oil, rice vinegar, sesame oil, soy sauce, spring onions, ginger and garlic. Place the salmon fillets in the marinade and turn to coat. Cover and marinate for at least 15 minutes, or up to one hour.
Preheat an outdoor barbecue for medium heat. Place the planks on the grate. The boards are ready when they start to smoke and crackle just a little.
Place the salmon fillets onto the planks and discard the marinade. Cover, and barbecue for about 20 minutes. Fish is done when you can flake it with a fork. It will continue to cook after you remove it from the barbecue.
Cedar planks for barbecuing can be purchased online or in specialty shops.