Season salmon fillets with lemon pepper, garlic powder, and salt.
Combine soy sauce, brown sugar, water, and vegetable oil until sugar is dissolved. Place fish in a large resealable plastic bag, pour soy sauce mixture over fish, seal, and turn to coat.Marinate for at least 2 hours.
Preheat grill for medium heat.
Lightly oil grill grate. Place salmon on the preheated grill, and discard marinade. Cook salmon for 6 to 8 minutes per side, or until the fish flakes easily with a fork.
Wrap it in foil and bake at 425° for approx. 15 minutes.