In large saucepan, bring water and 1 teaspoon of the salt to a boil. Add shrimp and scallops; cook 2 to 3 minutes or just until shrimp turn pink and scallops turn opaque. Reserve 2 cups of the poaching water; place in medium saucepan. Drain seafood; rinse with cold water to stop cooking. Refrigerate seafood until serving time.
Meanwhile, bring reserved 2 cups poaching water and 1 tablespoon oil to a boil. Remove from heat; stir in couscous. Cover; let stand 15 minutes.
Remove cover; fluff couscous with fork. Cool 10 minutes.
In medium nonmetal bowl, combine 1/2 cup oil, lemon juice, pepper and remaining 3/4 teaspoon salt; mix well. Add cucumber, onions, parsley, basil and cooled couscous; mix well. Refrigerate at least 1 hour or until serving time.
When ready to serve, line plates with lettuce. Spoon couscous mixture evenly onto lettuce. Top each with seafood. Garnish with lemon wedges.