Between sheets of plastic wrap, pound the chicken breasts to 1/2 inch thickness.
In a medium bowl, mix all the remaining ingredients until well blended. Reserve 1/2 cup of the mixture in a small bowl. Cover and refrigerate.
Spread the remaining sour cream mixture over both sides of the chicken breasts. Seal the coated chicken in a large food storage plastic bag, or in covered glass dish. Refrigerate for 1 to 4 hours.
Spray a grill rack with cooking spray or brush generously with oil. Heat the grill. Grill the chicken over medium heat for 10 minutes or until the chicken is no longer pink in center and a thermometer inserted in the center reads 165 degrees, turning once.
Serve the chicken with the remaining sauce on the side.