Clean and cut 500 grams of chicken into medium-sized pieces. Set aside.
Dry roast 2 tablespoons of coriander seeds, 1 tablespoon of cumin seeds, 1 tablespoon of fennel seeds, 1 teaspoon of black peppercorns, 4-5 dry red chilies, and 1 tablespoon of poppy seeds until fragrant. Cool and grind them into a fine powder to make the Chettinad masala.
Heat 2 tablespoons of oil in a pan. Add 1 teaspoon of mustard seeds and let them splutter.
Add 1 finely chopped onion and sauté until golden brown.
Add 1 tablespoon of ginger-garlic paste and sauté for 2 minutes.
Add 2 chopped tomatoes and cook until they turn soft and mushy.
Add the prepared Chettinad masala, 1/2 teaspoon of turmeric powder, and salt to taste. Cook for 2-3 minutes.
Add the chicken pieces and mix well. Cook for 5 minutes on medium heat.
Add 1 cup of water and bring it to a boil. Cover and cook on low heat for 20-25 minutes, or until the chicken is cooked through and the gravy thickens.
Garnish with chopped coriander leaves and serve hot with rice or roti.