Heat the oil in a heavy-bottomed pot over medium heat. Add the nigella seeds, fennel seeds, mustard seeds, fenugreek seeds, and cumin seeds. Sauté for 30 seconds until fragrant.
Add the thinly sliced onion and fry for 5 to 7 minutes until soft and golden brown.
Stir in the ginger paste, garlic paste, red chili paste, turmeric powder, and salt. Cook for 1 minute until the raw smell disappears.
Pour in the tomato puree. Increase the heat to high and cook until the oil begins to separate from the masala base.
Add the chicken pieces and sear on high heat until the meat is no longer pink.
Lower the heat, cover the pot, and let it simmer for 15 to 20 minutes until the chicken is tender and cooked through.
Remove the lid and stir in the whisked yogurt and slit green chilies. Simmer for an additional 5 minutes.
Turn off the heat, garnish with fresh cilantro, and serve hot with naan or rice.