Steps
1. In a pot, bring the water to a boil. Add in the lemongrass, ginger, garlic, and onion, and let it simmer for about 5 minutes.
2. Stir in the tamarind paste, chili paste, and sugar. Mix well.
3. Add the stingray fillet and cook for 10 minutes, or until the fish is cooked through and tender.
4. Add the tomato and season with salt to taste. Let it simmer for another 2-3 minutes.
5. Serve hot, garnished with fresh coriander.