Chop the chicken thighs into bite-sized pieces.

Slice the onion, chop the garlic, mince the ginger, and slice the green chillies.

Heat 1 tablespoon oil in a large skillet over medium-high heat.

Add the chicken pieces, season lightly with salt, and sear for 3-4 minutes until browned. Remove from the pan and set aside.

To the same pan, add the remaining 2 tablespoons of oil.

Add cumin seeds and mustard seeds, letting them sizzle for 30 seconds until fragrant.

Add the sliced onion and sauté for 6-7 minutes until golden and soft.

Stir in the chopped garlic, minced ginger, and green chillies. Cook for 2 minutes until aromatic.

Sprinkle in the turmeric, ground coriander, garam masala, and red chilli powder.

Sauté for 1 minute to toast the spices and release their flavors.

Pour in the canned chopped tomatoes, salt, and sugar.

Simmer for 8-10 minutes, stirring occasionally, until the sauce thickens and oil starts to separate.

Return the seared chicken (and any juices) to the pan.

Add water and stir everything together.

Cover and simmer on low heat for 15-18 minutes until the chicken is cooked through and tender.

Squeeze in the lemon juice and check seasoning, adjusting salt or chilli to taste.

Sprinkle with fresh coriander leaves just before serving.

Serve hot with steamed basmati rice, naan, or roti.