In a large saucepan, bring 450 ml / 16 fl oz of water to the boil. Add the potato and a little salt and cook over a medium heat for 10 minutes. Add the pumpkin and green chillies. Cover and cook for 10 minutes until all the vegetables are tender. Lower the heat under the pan and add the coconut milk, stirring gently. Add the beans and curry leaves, mix well and allow the beans to heat through. Serve warm.