1 (8 ounce) container plain yogurt...
3 tablespoons balsamic vinegar
8 thin-cut boneless, skinless chicken breast halves (about 1 1/2 pounds total)
1 tablespoon extra-virgin olive oil
1 medium-size onion, cut into 16 wedges
1/4 cup balsamic vinegar
2 tablespoons water
1 pound plum tomatoes, cored, seeded and chopped (about 4 cups)
1 teaspoon salt
1/2 teaspoon black pepper
8 ounces fresh mozzarella cheese (usually packed in water), cut into 1/2-inch cubes
1 cup loosely packed fresh basil leaves, chopped
1. For the Chicken: In a small bowl, whisk together the yogurt and balsamic vinegar until blended. In a plastic food-storage bag, combine chicken and yogurt mixture. Seal and turn the bag to coat. Marinate in the refrigerator for 20 minutes.
2. Meanwhile, heat a gas grill or grill pan to medium-high.
3. For the Tomato-Mozzarella Topping: In a large skillet, heat oil over medium heat. Add the onion and saute about 5 minutes or until onion is slightly softened and the wedges fall into pieces. Add the balsamic vinegar and water. Bring to a simmer. Reduce heat to medium-low; cook about 7 minutes until liquid is reduced and onion is tender.
4. Increase heat to medium-high and add tomatoes, salt and pepper. Cook for 2 minutes and remove from the heat. Let mixture cool for 2-3 minutes then stir in mozzarella cubes and basil gently.
5. Remove chicken from bag. Discard marinade. Gently rinse chicken and pat it dry with paper towels.
6. Spray grill with cooking spray or coat with oil. Grill for 6-8 minutes per side. Serve immediately. Serve chicken on platter with topping in the center and let guests spoon their topping on.