Heat the oil in a large frying pan and fry the onions gently on a medium heat for about 10 minutes, or until soft.
Add the garlic and ginger and cook for 2 minutes, stirring, then add the curry powder, cumin, coriander and vindaloo paste. Cook through for several minutes.
Add the tomato and potato and half the water and cook for a few minutes, stirring.
Add the chicken and cook for a further 5 minutes and then add the remaining water.
Partially cover the pan and continue to simmer until cooked, about 30 minutes.
Serve with steamed rice and greens.