Coat chicken breasts in yogurt and tandoori powder and grill on skewers until cooked, set aside. Make the sauce by chopping onions and garlic and ginger finely or use a food processor, then fry in a little vegetable oil for about 10 mins add to the blender and add tomato puree, spices and about a cup of water, blend to a smooth paste. Add all back to pan and add coconut milk plus one large onion sliced (kept from original few) and cook until thickened. Add at least another cup of water during the process. When the chicken is cooked add to the curry and add spinach, finally chop up some coriander to add to the dish.