1. Bring water and salt to the boil in a large pot.
2. Add washed yen choy leaves and boil for 15 minutes or until tender.
3. In a separate pan, heat the oil and cook the chopped onion until golden brown.
4. Add the chopped tomatoes and cook until soft.
5. Add the well drained yen choy leaves and stir to combine.
6. Add the coconut milk and continue cooking for about 10 minutes.
7. Adjust seasoning or add lemon juice to taste.