Place the scallops, lime juice, salt and sugar in a medium bowl and toss to coat. Cover and marinate in the fridge for 3 to 4 hours, or until the scallops have turned opaque and appear cooked through. Drain all but 1 Tbsp.of the liquid from the bowl. Add the remaining ingredients, except the salad greens and garnish, and gently toss. Cover and refrigerate for 1 hour more. Divide the salad greens among 4 decorative glasses or salad plates. Top with the scallop mixture, garnish with lime wedges and cilantro sprigs,and serve.