Arctic char, by the way, is very similar to salmon. If you like salmon, you'll probably like Arctic char. It's available both wild and farmed.
Season the fish. Coat in a small amount of olive oil.
Grill for 2 minutes per side over very high heat. It won't be cooked through because it's going to go into the sous vide later. Actually, if you wanted a simple dinner it might make more sense to just go ahead and cook it for a few more minutes and cook it all the way through. Nonetheless...
Immediately chill the fish. This stops the cooking, but more importantly, if the fish is not cold when you vacuum seal it, one of two things will happen: If you have an external vacuum sealer (FoodSaver, for example), the juice will get sucked out of the bag, which is bad. And if you have a chamber vacuum sealer, the bag will inflate like a balloon. This happens because as the pressure drops any hot water in the bag will boil, causing the bag to expand. This is pretty much the opposite of what you want to have happen for sous vide.
Vacuum seal and sous vide for 30 minutes at 138°F. The time is not critical, and you can cook it longer if necessary. In fact, that's why I prefer to finish off the fish in the sous vide instead of on the grill. My grill is inconveniently located down a flight of stairs from my kitchen so it's a pain to cook anything else that goes with grilled food. By pre-grilling it and finishing in the sous vide, it's much easier to have everything done at the same time with no fuss.
Since this was a simple meal I just served it with spicy green beans and rice.
The green beans are simple, too, because I pre-blanch the beans so all I need to do is toss them in a sauté pan with sesame oil, Thai chili pepper sauce, and soy sauce for a minute or two before serving.
The rice, white sushi rice, comes out of the rice maker, so that's simple, too.
So there's a lot of equipment involved, but the great thing is that it comes together so easily at the end and there's only one small sauté pan to wash. And, of course, it's delicious!