Carefully clean scallops of any roe, muscle, or brown connective tissue, which can become tough when marinated. Cut scallops into 1/4-inch horizontal slices.
Combine marinade ingredients in a small bowl. Add scallops and toss to coat. Marinate, covered, in refrigerator 5 minutes or as long as a half hour. (Any longer and the acid in the lime juice would overcook the seafood.)
Meanwhile prepare Watercress and Avocado Salad, reserving avocados.
To serve, divide dressed watercress salad among 6 serving plates. Arrange a circle of scallops in center of each and garnish with avocado slices along the side. Spoon leftover marinade over scallops and avocado. Serve cold.
c.1997, M.S. Milliken & S. Feniger, all rights reserved