Soak skewers in hot water at least 30 minutes. Prepare outdoor grill for direct grilling over medium heat.
Meanwhile, pull off and discard tough crescent-shaped muscle, if any, from each scallop. Rinse scallops well to remove sand from crevices and pat dry with paper towels.
From lemon, grate 1 1/2 teaspoons of peel and squeeze 1 tablespoon of juice. In a small bowl, whisk lemon peel and juice, oil, Dijon, and salt until blended. Set aside.
Thread 3 tomatoes and 2 scallops alternately on each skewer, beginning and ending with tomatoes.
Brush scallops and tomatoes with half of Dijon mixture; place on hot grill grate. Cook 7 to 9 minutes, turning several times. Brush with remaining Dijon mixture, and cook 5 minutes longer or until scallops are just opaque throughout.
188 Calories, 21 g Protein, 14.5 g Carbohydrates, 1 g Fiber, 340 mg Sodium. ★★ Vitamin B12.