Rub the fish steaks with the salt and turmeric, and set aside while you get all the other prep work going.
4 fish steaks (or fish fillets), ¼ tsp salt, ½ tsp ground turmeric
Prep Work
AromaticsPeel and halve the onion. The slice thinly.Peel the garlic and slice them width wise.Peel the ginger and slice into matchsticks.Bruise the lemongrass. Cut the bottom 10cm (4in), lose the top. Then, with the back of your knife, pound down hard on the thick end. This will release the aroma.Halve the chillies lengthwise. If using birds eye, leave them whole.
1 large onion, 5 cloves garlic, 5 cm ginger, 1 lemongrass, 2 green chillies, 2 red chillies
The VegetablesCut the carrot into matchsticks too.Do the same with the cucumber, but losing the middle, seedy bit.Quarter the tomatoes.
1 medium carrot, 5 cm length of cucumber, 2 medium tomatoes
Let's get Cooking
Heat the oil in a deep frying pan or wok on medium-high heat. Brown the fish steaks for 1 minute on each side. It's an oily fish so you'll see tiny white "blobs" forming, don't worry about it.
4 Tbsp vegetable oil
Take them out and place them on a plate lined with kitchen paper, to absorb excess oil.
If there is a lot of oil left, pour it out, reserving only about 2 Tbsp of it in the pan. Reduce the heat to medium and fry the mustard seeds for 10 seconds.
½ tsp black mustard seeds
Tip in the onions and fry for 3 minutes.
Add the garlic, ginger and lemongrass and fry for 30 seconds.
Add the vinegar, water, carrot sticks and salt, and stir to mix. Bring it to simmering point. Then cover and cook for 3 minutes.
4 Tbsp clear vinegar, 125 ml water, ½ tsp salt
Gently add the browned fish into the vinegar mix, pushing aside the vegetables, and resting each steak in a dip. Use a ladle and gently scoop over some of the liquid and vegetables.Tuck in the cucumber sticks, chillies and tomatoes along the sides and between the fish.Bring back to as simmer, cover and cook for 5 minutes.
Check seasoning and add more salt if you need it. Scatter coriander leaves, if using, and leave to rest for 5 minutes before serving.