Preheat grill to high. Sprinkle BBQ seasoning on salmon. Combine together all ingredients for the crust mixture and spread generously over the flesh side (not skin side) of each fillet. Season soaked planks with sea salt and place on grill, close lid and heat for 3 to 5 minutes until they start to crackle and smoke.
Carefully lift lid and place salmon fillets on hot planks, skin side down. Close lid and plank-bake salmon for 12 to 15 minutes for medium doneness. Check periodically to make sure that planks are not on fire. Use spray bottle to extinguish any flames. Squeeze lemon over fillets. Carefully remove planks from grill and transfer salmon to serving platter.
