Prepare grill or heat broiler.
Whisk together vinegar, olive oil, garlic, 1/4 teaspoon of the salt, and the pepper in a small bowl. Set dressing aside.
Alternately thread scallops, artichoke hearts and tomatoes on 4 skewers. (If using wooden skewers, soak for 30 minutes.) Season with the remaining 1/2 teaspoon salt. Brush skewers lightly with 3 tablespoons of the dressing.
Grill skewers over hot coals or broil for 4 to 6 minutes, turning occasionally, until scallops are white; dont overcook.
Toss together radicchio, cucumber, green onion, lettuce and dressing in large salad bowl. Arrange salad on plate with skewers on top. Makes 4 servings.