Prepare the scallops. Carefully trim, removing the hard muscle. Cut into 1/4 inch slices. In a small bowl, mix together the olive oil, lime juice, shallots, cilantro, salt and pepper; toss with the scallops. Cover, and refrigerate for 1/2 hour (the acid from the lime juice will cook the scallops). Drain, reserving the marinade.
Prepare the salad. Place the watercress in a large salad bowl. Whisk together the olive oil, lemon juice, salt and pepper; toss with the watercress. Divide onto six serving dishes, top with scallop slices and 1/4 teaspoon of the marinade. Serve cold.
Per Serving: 107 Calories (kcal); 3g Fat (trace Sat, 2 Mono, trace Poly); 14g Protein; 5g Carbohydrate; 25mg Cholesterol; 404mg Sodium. Food Exchanges: 0 Grain (Starch); 2 Lean Meat; 1/2 Vegetable; 0 Fruit, 1/2 Fat, 0 Other Carbohydrates.