Place a large heavy based pot over medium heat. Add in the oil, garlic, galangal and ginger and fry until fragrant. Add in the duck and fry in the oil for 5-7 minutes.
Add in the hot boiling water to the pot and bring it up to a boil. Add in the mustard greens, tomatoes, tamarind and chillies and simmer for a further hour.
If you like it more sour, just add in more lemon juice.
