Pre heat oven to 180 degrees.
Fry the onions in a frying pan for a couple of minutes. Add the minced garlic and finely chopped chili's and cook for 3-4 minutes. Add so the diced tomatoes, yoghurt, coconut milk, garam masala and lime juice, let cook for about 10 minutes on low heat.
Cut the chicken in small to medium dices and add to a casserole. Pour the tikka masala sauce on top and stir so the chicken is coted in sauce. Leave in oven for 1-3 hours.
Garnish with fresh coriander and serve with rice.