Make 2 slits in the chillies or peppers making sure the stem is intact.
Heat oil in a kadhai or wok over medium-high heat. Add chicken and fry them on each side until browned (approximately 3-4 minutes each side). Don't overcrowd the pan, fry them in batches. Transfer the chicken to a plate and set aside.
Add the chillies or pepper, saute them for a minute or two and set them aside.
Add mustard seeds to the oil and when they begin to sputter, add cumin seeds, fennel seeds, fenugreek seeds and nigella seeds (if using).
Saute them for 10-20 seconds and then add the chopped onion slices and fry them till they soften (approximately 10-12 minutes).
Add garlic and ginger and fry them for a minute or so.
Add chopped tomatoes and fry them till the mixture becomes mushy and begins to leave oil.
Add yogurt, salt, garam masala, coriander - cumin powder and chilly powder and mix well. Add water as needed to get it to the consistency you desire.
Add the chicken back to the wok and continue cooking on medium heat till it is done (approximately 10 minutes).
Add chillies or peppers along with lime juice. Cover the wok and let it simmer for another 5 minutes.
Garnish with coriander leaves and serve it with hot with roti or rice