For this dish, you'll need cedar grilling planks, available at some supermarkets and at surlatable.com.
Soak planks in water 2 hours. Remove and sprinkle with a thin layer of salt (about 1 teaspoon). Preheat grill for indirect heat, with coals to 1 side (or medium heat on a gas grill).
Place salmon, skin side down, on planks and season with salt and pepper. Spread 1 tablespoon mustard in a thin layer on top of each fillet. Drizzle each with 1 teaspoon honey; spread evenly.
Place planks on indirect side of grill; cover. Cook until fish reaches 135 degrees and is partly opaque in center, about 25 minutes.