Marinate fish steaks with half turmeric powder and salt for 10 minutes.
Heat mustard oil in a skillet and shallow-fry fish steaks until golden on both sides; remove.
Add finely chopped onions, ginger paste, and garlic paste to oil; sauté until deep golden.
Add chopped tomato, remaining turmeric, red chili powder, whisked yogurt, and salt; cook until oil releases.
Add water and fried fish, simmer covered for 10 minutes, and finish with garam masala.