Marinate Tilapia fishes with ½ tsp of turmeric powder and a bit of salt. Keep them aside for 10 minutes.
Place a wok on the clay stove and pour 3 tbsp of mustard oil into it.
Fry both sides of the tilapia fish (no need to deep fry) and then take them out and place them on a plate.
(Pro tip: Avoid over-frying the fish, as it can make the fish dry and firm.)
Add black cumin seeds to the remaining oil in the wok.
Add finely sliced onions and fry them until they turn light brown.
Add Kashmiri red chili powder and a little bit of turmeric powder. Sauté for a few seconds.
Add a little bit of water and stir well.
Add mustard paste and sauté for 5 minutes. Then, add water according to desired gravy consistency.
(Pro tip: Cook the mustard paste over medium-low heat to mellow its raw pungency while preserving its distinctive flavor.)
Add salt and the green chilies.
When the spicy mustard gravy comes to a boil, slide the fried tilapia fish one by one into the wok.
Cook for a few minutes. Add 1 tablespoon of mustard oil for flavor. Place a lid on the pan.
Remove the lid after 2 minutes.
Tilapia sorshe jhal is ready.