Rub the fish with olive oil and cover with the gin salt.
Heat the charcoal grill to medium-high heat. Light a chimney starter filled with charcoal. When charcoal is fully lit and covered with grey ash, pour it out. Then, carefully set the coals on one side of the charcoal grate.
Put the grill grate in place, and cover the grill. Let it preheat for about 5 minutes.
Clean the grill and oil it. Using direct heat, place the wooden planks on top of the hot part of the grill until it begins to char and smoke, turn the grill down to medium heat
Turn over the planks and move them to the cool side of grill to use the indirect heat. Then, arrange the fish on top of it. Cover the grill and let it cook until the fish is opaque and begins flaking. This should take about 15 to 20 minutes.
Take the fish from the grill. Your cedar-plank whitefish is ready to serve!