Blend all ingredients except the fish and lemon in a mixing bowl. Transfer, label, wrap tightly, and store at room temperature until needed.
Sprinkle both sides of the salmon evenly with the dry rub (1 1/2 tsp to 2 tsp per 6-8oz fillet) and then press the seasonings into the flesh. Refrigerate, uncovered, for at least 2 hours and up to 12 hours before cooking.
Soak the untreated 3/8-inch cedar plank in water for 1 to 2 hours. Preheat the grill on high. Place seasoned salmon fillets onto the plank (making sure they're not touching) and squeeze lemon over them. Place the planks on the grill, lower the heat to medium, and cover. Cook for 8 to 12 minutes, depending on the fillets' thickness; their internal temperature should be 120Â°F.
Remove the plank from the grill. (Careful! Embers may stick to the bottom of the plank.) Serve with a hunk of lemon.