1.Season salmon fillets with garlic powder, salt and pepper on all sides.
2. In a small bowl, combine soy sauce, water, vegetable oil and sugar. Stir well until sugar is dissolved.
3. Place salmon in a plastic bag, pour in the marinade, close tightly (removing excess air), and toss the bag around to coat fish completely with the marinade. Refrigerate for 2 hours or more.
4. Preheat the oven's broiler and set the oven rack about 6 inches from the heat source. Remove salmon from the marinade and arrange on a baking sheet, previously covered with foil. Discard the marinade.
5. Cook until lightly browned and flakes easily with a fork, about 10 minutes.