Heat oil in a pan and add the mustard seeds
When they start to pop, add the dried chillies and curry leaves and saute for a few mins
Add onions and stir over moderate heat for around 5 minutes until onions are soft
Stir in coriander, garam masala, turmeric and chilli powder
Add tomatoes and cook for 5 more minutes
Add potatoes, mix well and cook for another 5 mins
Add green beans, cook for a minute and then lower the heat and add the coconut milk and water and salt to taste
Stir well, cover and cook for around 20 mins until the potatoes and beans are tender
Check for seasoning and eat with rice and roti!