Toss the onion with the olive oil, and spread on a grill pan.
Place the onion on the grill. Grill for 10 to 15 minutes, stirring occasionally. Remove from grill when the onion has started to brown. NOTE: If you don’t have a grill pan for the onions, you could grill larger onion slices and chop them after grilling. You could also simply use 1/4 cup raw diced onions.
In a bowl, combine the pineapple, onion, jalapeño pepper, 1 tablespoon olive oil and lime juice. Salt and pepper to taste, stir and set aside while you grill the fish.
Combine the orange juice and soy sauce in a large bowl.
Rinse and pat dry the arctic char, and place it in the bowl with the OJ and soy sauce mixture. Turn to coat both sides of the fillet.
Bring the grill heat back to 400 degrees. Gently shake excess marinade from the char, then place it on the grill skin side down.
Grill the char, covered, for 3 minutes. Carefully turn the char over, and grill skin side up for three more minutes. Remove the cooked char to a platter.
Portion the arctic char, and serve topped with a generous serving of the pineapple salsa. Enjoy!