Preheat oven to 160°C.
1 Wash chicken thoroughly and dry with paper towels. Sprinkle with salt and pepper, add masala and rub all over the chicken. Set aside.
2 Braise the onion in oil in a small pot until soft. Add mustard seeds, chilli powder, curry leaves, ginger and garlic. After 3 minutes add tomatoes and water and simmer for 20 minutes until tomatoes have softened into a thick sauce. Add salt to taste. Set aside.
3 Grind the remaining dry spices with oil, rub onto chicken. Put in a roasting dish and roast for 30 minutes.
4 Remove the chicken from the oven, put over medium coal fire (or grill in an oven) and turn every 7 minutes for 21 minutes until evenly browned.
5 Cut the chicken in half, heat up the masala sauce and spoon over the chicken. Garnish with fresh coriander and serve with rice or carrot salad.