Season salmon fillets with lemon pepper, garlic powder, and salt.
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.
Preheat grill for medium heat.
Lightly oil grill grate. Place salmon on the preheated grill skin down. Leave until the skin is propertly charred.
Turn over and grill until charred. Baste with sauce.
Cook salmon for 6 to 8 minutes per side, or until the fish flakes easily with a fork.