Put a medium sauté pan for which you have a lid on a medium-high heat. Once hot, add the olive oil, spring onion whites and lime leaf, sauté for two to three minutes, until softened, then add the tomato paste and cook, stirring, for two minutes more, until the oil turns red; make sure the paste doesn’t go dark, or the soup will turn out bitter.
Stir in the chilli flakes, stock, tamarind, soy sauce, ginger, palm sugar and an eighth of a teaspoon of salt, cover and bring up to a simmer. Turn down the heat to medium-low and leave to cook for 25 minutes.
Add the beansprouts to the pot, and cook for another five minutes, just until they have softened.
Divide the shredded cabbage between four bowls, ladle the hot soup over it and serve topped with the spring onion greens and the sliced red chilli.