1. Season salmon fillets with lemon pepper, garlic powder, and salt.
2. In a small bowl, stir together soy sauce, brown sugar, water, and vegetable oil until sugar is dissolved. Place fish in a large resealable plastic bag with the soy sauce mixture, seal, and turn to coat. Refrigerate for at least 2 hours.
3. Preheat grill for medium heat (300 to 350-deg F)
4. Lightly oil grill grate. Place salmon on preheated grill, and discard marinade. Cook salmon for 6 - 8 minutes per side, or until the fish flakes easily with a fork.