Cut the fish into 2 cm cubes. To aid in the cutting process, you can partially freeze the fish. Season with half the salt and pepper.
In a frying pan, add a tablespoon of the oil and heat on medium high.
Pan fry the fish cubes until lightly golden and cooked through but still tender, about 5-6 minutes. Turn the fish cubes to cook on all sides during the frying process. Remove the fish from the pan and reserve.
Next prepare the tempering oil. Add the remaining oil to the pan and heat on medium heat.
Add the onions, asafoetida (if using), curry leaves, remaining salt and pepper and cook for 5 minutes until lightly golden.
Add in the chillies, sliced garlic, fenugreek seeds and mustard and cook for another couple of minutes.
Last add the turmeric and lemon juice and stir until combined before turning off the heat.
Combine the fish and oil and keep in a glass container for upto 10 days.
Serving suggestion: serve on crusty baguette slices with microgreens or pickled cucumber ribbons.