first, soak the planks in a sink of water, for at least four hours. i used a cast iron pot lid to weigh the planks down in the sink.
the planks absorb the water and this prevents them from burning on the grill, and also allows them to steam cook the fish. next, prepare the whitefish. i used lemon pepper and herb seasoning, and a bit of parsley after spraying them with canola oil.
place the planks on the warm grill, close the cover and allow to begin to smoke. then, turn the planks over and brush with grape seed or olive oil. place the fish, skin side down first, and close the grill cover, cooking for about 12 minutes. then, open the grill, turn the fish over on the planks and continue to grill until done. total cooking time should be about 25 minutes. we moved the planks off of the direct heat to the sides of the coals after the first 1/2 of the cooking process. the fish will be flaky and white throughout the body, and begin to separate from the skin when done.