For Marinating and Frying Fish

1. Clean the fish by rinsing it with water and tamarind pulp. Gently massage the tamarind pulp onto the fish pieces before washing them with water to remove any pungent smell. 
2. After cleaning, pat the fish dry and proceed with marinating.
3. Rub turmeric and salt evenly on the surface of the cut pieces of fish. Massage thoroughly to ensure the spices penetrate the flesh of the fish.
4. Start by heating the oil on medium-high heat, then fry the marinated fish until it achieves a gorgeous golden brown color. Remember to flip it after 3 minutes.
5. Drain the fish pieces of excessive oil using a kitchen towel , then set them aside to cool down.

For making Soup

1. In a shallow pot, heat 1 tablespoon of oil over medium-low heat. You can use the oil that was previously used to fry the fish.
2. When the oil is hot enough, toss in the mustard seeds.
3. After the mustard seeds have popped, add in the onion, garlic, and ginger.
4. Cook the ingredients until they are lightly browned, which may take about 1-2 minutes, but be careful not to overcook or burn them.
5. Meanwhile, make tamarind juice by soaking the pulp in water. 
6. Then, use your hands to crush and dissolve the pulp before straining out any leftover residue with a colander.
7. Add the tamarind juice into the pot and mix well. 
8. Take a lemongrass, crush it with the back of the knife and add to the soup.
9. Immediately, toss in the chillies, tomatoes and fried fish right away.
10. Stir and bring the soup to simmer.
11. Let the soup simmer for an additional 2 minutes before serving. Enjoy it with a side of steaming hot rice.