Preheat broiler.

Place diced tomatoes, garlic and capers in a glass bowl and season with 1/8 teaspoon each salt and pepper. Let stand for five to 15 minutes. Stir in olive oil, vinegar and mustard. Remove four tablespoons of the liquid and set aside.

Place chicken in a large baking dish or pan with sides. Brush tops with reserved relish liquid and season with remaining salt and pepper. Cook seven minutes, remove chicken from oven, turn the pieces and add tomato relish to the pan, brushing some of the juices on chicken tops. Cook six to nine more minutes, until the internal temperature in the thickest part of the chicken reaches 165 Fahrenheit on an instant read thermometer. Transfer chicken to a serving platter. Stir basil into tomatoes to wilt. Spoon tomato relish over chicken breasts to serve.