Position knife blade in food processor bowl. Combine first 6 ingredients in processor bowl. Process until smooth. Set aside 1/4 cup tomato mixture.
Place chicken in a large heavy-duty, zip-top plastic bag. Pour remaining tomato mixture over chicken. Seal bag; turn bag to coat chicken. Marinate in refrigerator 8 hours.
Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Remove chicken from marinade, discarding marinade. Coat tomato halves with cooking spray. Place chicken and tomato halves on rack; grill, covered, 5 to 6 minutes on each side or until chicken is done and tomato is cooked but still slightly firm. Place chicken on 4 individual serving plates; top each chicken breast half with 1 tablespoon reserved tomato mixture. Arrange 2 grilled tomato halves on each plate with chicken.