Poach shrimp and scallops in a medium saucepan of boiling water 1 minute. Drain and refresh under cold running water. Whisk together juices, oil, and 1 teaspoon each salt and sugar. Whisk in green onion and cilantro. Toss seafood in dressing. Refrigerate 30 minutes before serving. Season to taste with freshly ground black pepper. Serve over Bibb lettuce.