Using a plank to grill fish keeps it from sticking or falling through the grate and imparts a subtle smoky flavor to the salmon. You could also use mahi-mahi or Pacific halibut in this recipe.
Soak a grilling plank in water for 2 to 4 hours.
Meanwhile, combine soy sauce, sake (or white wine), mirin, sugar, scallions and ginger in a small saucepan and bring to a boil. Remove from the heat and let cool to room temperature.
Place salmon in a shallow dish and pour the marinade over it. Place lemon slices on top. Marinate in the refrigerator for at least 30 minutes but no more than 2 hours, turning the fish once or twice.
Preheat grill to medium-high.
Place the soaked plank over direct heat on the grill and heat for 2 minutes. Move the plank so it’s over indirect heat. Remove the salmon from the marinade, place it skin-side down (if using fillets) on the hot plank and replace the lemon slices on top. Close the lid and cook until the fish is just cooked through, 10 to 15 minutes. Use the plank as the serving platter, if desired.
Make Ahead Tip: The salmon can be marinated for up to 2 hours