Put the whole spices & garam masala into a blender and grind for 30 seconds before adding the chilli, garlic, ginger and lemon juice. Grind to a paste
Transfer the spice paste to a shallow dish. Add the yogurt, ½ tsp salt and stir well to mix. Set aside.
Score the flesh of the chicken deeply. Put the chicken in a single layer in the dish then spoon over the marinade over the chicken and brush it into the cuts. Cover and marinade in the refrigerator for at least 4 hours or preferably overnight
Put the chicken on a griddle or barbecue. Cook, turning often, for 30 minutes or until the juices run clear when pierced with a skewer or fork. Serve hot with a sauce made from yogurt & fresh mint