Wash and marinate fish pieces with turmeric and salt for 10 minutes.
Heat mustard oil in a pan until hot, then lightly fry the fish pieces until golden. Remove and set aside.
In the same oil, add potatoes and fry lightly.
Add chopped tomatoes and cook until soft.
Add turmeric powder, cumin powder, and salt; mix well.
Pour in water and bring to a boil.
Add fried fish pieces and simmer for 8–10 minutes.
Cook until potatoes are tender and flavors blend well.
Adjust seasoning and consistency as needed.
Serve hot with steamed rice or enjoy as a light fish soup.