2) The next day, rinse the beans, cover with 700ml of fresh water and bring to the boil over high heat. Reduce the heat and simmer covered for 30 minutes, skimming off any foam.
3) Stir in the onion and simmer 30 minutes more. Add the garlic, oregano, cumin, and dried chilli flakes, and simmer uncovered for 30 minutes, stirring occasionally.
4) Stir in the sugar and vinegar and season to taste with salt and pepper. Turn out into a large serving bowl and garnish with chopped spring onions.