- Place grilling planks in a shallow baking dish and cover with cold water and a splash of white vinegar. Submerge planks in water by weighting them down with a small heavy saucepan or can. Soak for at least 2 hours and up to 12 hours.
- In another shallow glass or ceramic baking dish, lay salmon fillets in a single layer. In a mixing bowl, whisk together red wine vinegar, olive oil, honey, garlic, rosemary, salt, and pepper. Pour marinade over salmon, and allow salmon to marinate in refrigerator for at least 30 minutes and up to 1 hour.
- Preheat grill on medium heat for about 10 minutes. Remove planks from water and pat dry. Remove the salmon fillets from the marinade, discarding marinade, and place atop planks.
- Place planks on preheated grill with lid closed. Grill for about 10 to 15 minutes, or until salmon is cooked to desired temperature (about 135 degrees for medium). Remove from grill and garnish with rosemary sprigs and lemon slices.