Preheat the grill to high. To make the marinade, put the marinade ingredients into a large bowl and whisk together well. If you prefer, put the ingredients in a blender or food processor and process until well blended. Transfer to a bowl large enough to hold all the chicken breasts.
Score 2 slits on each side of the chicken breasts. Place them in the marinade, turning to coat and rubbing the marinade into the slits. (If you have time, leave the chicken to marinate in the fridge overnight.)
Brush the grill rack with oil, then place the chicken breasts on top. Grill for 12â€“15 minutes, turning and basting with the remaining marinade, until the juices run clear when the chicken is pierced with a knife, and the marinade is beginning to look slightly charred.
Meanwhile, combine all the ingredients for the raita in a bowl. Stir well to mix. Spoon the raita into a serving bowl.
Transfer the chicken breasts to a serving plate. Add lemon or lime wedges and garnish with coriander sprigs. Serve with the raita on the side.