Prepare the Chettinad Masala: Dry roast the coriander seeds, cumin seeds, fennel seeds, black peppercorns, dried red chilies, turmeric powder, fenugreek seeds, cinnamon, cloves, cardamom, and star anise in a pan until they become aromatic. Add the grated coconut to the pan and roast until it turns golden brown. Let the mixture cool down and then grind it into a fine powder. Set aside.

Cook the Chicken: Heat oil or ghee in a large pan. Add mustard seeds and allow them to splutter. Add chopped onions and sauté until they turn golden brown. Mix in the ginger-garlic paste and curry leaves, sautéing until the raw smell disappears. Incorporate the chopped tomatoes and cook until they become soft and mushy. Add the prepared Chettinad masala to the pan, stirring well to combine with the onion-tomato mixture. Add the chicken pieces, ensuring they are well coated with the masala. Cook for about 5-7 minutes. Pour in the water, season with salt, and bring the curry to a boil. Then, reduce the heat and simmer covered until the chicken is tender and the oil separates from the gravy.

Garnish and Serve: Garnish the curry with fresh coriander leaves. Serve hot with steamed rice, roti, or dosa.