In a glass dish not too deep, mix all ingredients, except the chicken breasts and yogurt and garlic sauce. Add chicken breasts and flip to coat well. Cover the dish with a plastic wrap and let marinate in the fridge for 2 hours.
Set the barbecue to medium-high heat. Put chicken breasts on a greased grill (keep the marinade), close the cover of barbecue and cook for about 7 minutes (baste the chicken breasts with the marinade a few times). Flip the chicken breasts and keep cooking for about 5 minutes or until the chicken is golden and not pink inside. Serve with yogurt and garlic sauce.
Yogurt and Garlic Sauce : In a bowl, mix yogurt with sour cream, parsley, garlic. Add salt and pepper. Cover and put in fridge for at least 4 hours.