- Marinate fish with 1/8 cup of mustard oil, turmeric and salt.
- Blend Greek and sweet yogurt with 1/8 cup of mustard oil, ginger & garlic pastes, chili paste, garam masala powder and salt to taste.
- Stir water and vinegar into mix and combine with fish.
- Heat remaining oil in a pressure cooker and sputter nigella seeds and minced green chilies, add onions and remove from heat.
- Layer fish pieces over bed of onions and pour the yogurt mixture over fish.
- Place pressure cooker over high heat and bring to a boil.
- Cover and bring up to pressure, lower heat to minimum/lowest setting and leave to cook for 1.5 hours.
- Allow pressure to release naturally and if there is too much gravy, uncover and simmer over medium heat until reduced.
- Garnish with minced cilantro and slit chilies.