Add the potato long beans, and all the spices (salt, red chilly powder, and turmeric).
Let the vegetables cook at low heat for about 1/2 hour, stirring occasionally to make sure they do not stick to the bottom of the pan. If the vegetables have not softened, add some water (enough to cover the vegetables) and let it cook some more.
Once the long beans and potatoes have softened, add some tamarind juice and let it cook for a few more minutes.
Remove from heat and add the coconut milk before serving.