Blend Onion, Salt, Turmeric, Chilli Powder, Coriander Powder and Cumin Powder in a blender without adding any water.
Apply the above mixture on the fish slices on both sides and marinate for 15 to 30 minutes.
Heat oil in a broad pan and shallow fry the above marinated fish slices using medium flame.
Flip both sides and cook thoroughly until the onion in the masala leaves the raw taste and the oil separates out. Do not cook too much also as the fish may become hard if the entire moisture is taken out due to excess cooking.
This fish fry will be very soft. The masala around the fish can be mixed with rice. It tastes excellent. More onion can be added to get more masala.