Here is a quick little guide line for cooking either Arctic char or wild Pacific caught salmon.

Buy fish in whole fillets with the skin on.
Remove the belly of the fish using a sharp knife - all you have to do is run it across where the thin belly meets the meatier flesh of the fish.

You want to remove the belly because it cooks much faster, so once you have removed it you can cook it along with your regular size fillets then eat it while you are barbecuing if you are so inclined, because it cooks so fast and it is a nice cook's snack.

Once belly is removed, portion the now evenly sized fish. An easy cheat is after you make your first portion, put that piece of fish on the whole fillet to use as a cutting guide so all your portions are roughly the same. And note: the tail bit will always be a touch smaller (maybe one for the kids).

Fish portions

Fish portioned and ready to barbecue (Mike Green)

(the grill will be open this whole time, don't shut it and overcook your fish)
Heat grill on high heat. Pat the fish on both sides with a paper towel so it is bone dry then rub fish with a bit of oil on each side (so it won't stick) and season with salt. 

Clean grill with either a grill brush or half an onion so it is nice and clean and doesn't have any bits that can make the fish stick. Place your individually portioned fillets skin side down and cook, depending on their thickness, for approximately five minutes on the skin side. 

Flip once the edges of the skin have started to crisp up, and the flesh on the bottom has begun to change to a lighter colour, working its way to the top of the uncooked flesh. 

Gently (using a flipper and not tongs!) turn the fish over, by placing your flipper between the skin and the grill and guide it flesh-side down with your hands. The flesh side should only take a minute or so and the resulting fish should be just flaking on the outside, while the inside still has a touch of pink to it (you can think of it like a medium steak). After a minute on the flesh side, very gently slide the fish onto your flipper. 

Serve the fish with the crispy skin facing upwards. You'll look like a pro this way, and it is a great way to introduce your dinner guests to the wonders of crispy fish skin.