Soak the planks in water for at least 1 hour. You will need to weight the planks to be sure they stay submerged.
Stir together the rice vinegar, sesame oil, soy sauce, ground ginger, and garlic powder. Add the oil and stir well, using a fork.
Place the salmon fillets in a ziplock bag and add the marinade.
Marinate for at least 15 minutes, if you can...try for 45 minutes.
Preheat an outdoor grill for medium heat or about 350 degrees.
Place the planks on the grate and close the grill.
Wait for the boards to smoke and crackle just a little and then Place the salmon fillets onto the planks, skin side down, save the marinade.
If desired, add a slice or two of fresh lemon to the salmon.
Cover, and grill for about 15 minutes. Maintain a medium heat or 350 degree temperature, opening the grill as little as possible.
After 15 minutes, brush with saved marinade and grill for another 5 minutes or until done.
Fish is done when you can flake it with a fork. Don't overcook it. It will continue to cook while it rests.
Remove it from the grill and let it rest.