Mix the rum and water in a large container and submerge the planks in the water for 30 to 45 minutes, allowing the planks to become soaked.
Meanwhile, in a medium-size bowl, mix together the sugar, ginger, coriander, salt, cinnamon, and lemon juice to create a paste. Spread spice mixture evenly on top of the flesh side of salmon (not skin side). Refrigerate for 30 minutes and up to 1 hour.
Preheat the grill over medium-high.
Remove the fillet from the refrigerator and arrange on the planks, unseasoned side down. Put the planks on the grill and cook until the flesh is firm to the touch, allowing the plank to smolder, not burn, about for 30 to 40 minutes. Once the salmon is cooked, remove planks from the grill, with hot pads, to a serving platter and allow it to rest for 10 minutes before serving.
The salmon can also be prepared with the same spice rub and baked for 30 minutes in a preheated 350 degree F oven without a plank.