Heat the oil in a large non-stick frying pan, add the onion and fry for 2 minutes until soft. Add the potatoes, garlic, cumin and chilli and cook for a further minute, stirring.
Add the chicken, tinned tomatoes, then half fill the tin with water and add this to the pan. Bring the mixture to the boil then simmer uncovered for 14 minutes until the potatoes are tender and the sauce thickened slightly.
Stir in the coriander and season to taste. Serve in bowls with green beans.