Combine first 6 ingredients in a medium bowl, stirring well. Cover and set aside.
Combine concentrate and next 5 ingredients; reserve one-half of mixture. Pour remaining mixture into a heavy-duty, zip-top plastic bag; add fish. Seal bag, and shake lightly until fish is well coated. Marinate in refrigerator up to 3 hours, turning bag occasionally.
Remove fish from marinade, discarding marinade. Coat a nonstick skillet with cooking spray; place over medium-high heat until hot. Add fish; cook 2 to 3 minutes on each side or until browned. Add reserved juice mixture to skillet. Bring to a boil; reduce heat, and simmer 10 to 12 minutes or until fish flakes easily when tested with a fork.
Bring 1 1/2 cups water and salt to a boil in a small saucepan; stir in couscous. Remove from heat; cover and let stand 5 minutes. Fluff with a fork.
To serve, place couscous evenly on 4 plates; top couscous with fish. Spoon any remaining pan juices over fish and couscous. Top evenly with reserved pineapple mixture.