At least 2 hours before you are planning to cook your fish soak your cedar plank in water. You may need to place a can or other heavy object on your plank in order to keep it submerged.
Heat your charcoal or gas grill to medium heat (approximately 350 degrees Fahrenheit)
After your plank has soaked for a minimum of 2 hours, remove it from the water and place your salmon filet on it, skin side down. If you are using skinless salmon, brush a little bit of olive oil on the plank before placing the fish on it.
Brush some olive oil on the top of your salmon. Sprinkle with salt and oregano. Place the lemon rounds on top of your fish along with the fresh rosemary sprigs.
Transfer the plank with the salmon carefully to your grill. Cook for approximately 12 - 15 minutes, until uniformly pink on the inside. Start checking your salmon at the 12 minute mark (cooking time will vary depending on the actual heat of your grill, and the thickness of your filet).
Once done, remove the plank and the salmon from the grill and set aside. To serve, you can present the entire filet and portion it out on the table. Otherwise, portion it out prior to serving. If your filet had skin on it, the skin will typically remain on the plank as you lift off the salmon meat.