You can buy cedar planks for cooking salmon at many grocery stores.
If you can't find one at a grocery store, make sure the cedar you use has no wood preservatives or other chemicals in it, unless you're into eating that sort of stuff.
Might I recommend a glass of turpentine as a lovely accompanyment if you use preserved wood.
Start the BBQ and preheat to HIGH.
Rub the filets all over with olive oil.
Sprinkle them with fresh dill and onion.
Drizzle with juice from the fresh lemon.
Sprinkle the cedar plank with the salt and place it on the now hot BBQ grill.
Leave it there for about 3 minutes, until it appears mostly dry on top (remember, it was soaking in water and should be quite wet....) Place your salmon filets (skin side down if the skin's still on them) on the plank.
Turn down the BBQ to low.
Drizzle some real maple syrup over the filets.
This is the secret ingredient.
Not Aunt Jemima.
Cook on low for about 10-15 min depending on the size of the filets.
When it appears the salmon is done ie.
flakes easily, slide the filets off the cedar plank onto the BBQ grill, skin down.
Crank up the BBQ to high, put some more maple syrup on top and cover for about 2 minutes.
This should finish off the salmon nicely, leaving delicious filets ready to eat, and skin that peels off easily if you don't like to eat it.