Make the marinade by combining the yogurt, olive oil, lemon juice, salt and spices.
Add the chicken breasts and marinate in the fridge for 20 minutes.
While the chicken is marinating, make the yogurt sauce by combining the yogurt, lemon juice, olive oil, mint and green onion in a small bowl. Salt and pepper to taste.
Grill the chicken (discard the marinade) on a lightly oiled grill, turning it from time to time until the meat is fully cooked (10-12 minutes). Put the chicken in a plate.
Pour the yogurt sauce over the chicken and serve with a summer salad.