Marinate the fish with a little turmeric powder and salt. Heat mustard oil in a frying pan, fry the fish till light brown. Keep aside on a kitchen absorbent towel.
To the same pan, add the remaining oil, when smoking hot, throw in the fenugreek seeds and green chillies. Allow the spices release their aroma.
Now add the lauki cubes, turmeric powder and salt, saute for 2-3 minutes.
Add the tomatoes, cook for another 2-3 minutes.
Add 1 1/2 cups of warm water. Give a nice loving stir, bring the curry to a gentle simmer.
Adjust seasonings, gently add the fried fish and cook for a further 5-6 minutes till the lauki is tender.
This curry shall have a runny consistency, feel free to add more warm water if needed.
Serve with rice.