Heat oil in a large pot over medium heat. Add mustard seeds and cumin seeds and let them splutter.
Add chopped onion and sauté until translucent.
Add minced garlic and grated ginger, and cook for a minute until fragrant.
Add coriander powder, turmeric powder, and chili powder. Stir well to combine.
Add chicken pieces to the pot and brown them on all sides.
Add chopped tomatoes and cook until they break down.
Pour in the coconut milk and add curry leaves. Stir well and season with salt.
Cover the pot and simmer on low heat for about 30-40 minutes or until the chicken is cooked through and the sauce has thickened.
Taste and adjust seasoning if needed.
Garnish with fresh cilantro before serving.
Serve hot with steamed rice or roti.
Enjoy!