Place the lentils in a large pan with 400ml water. Add turmeric and tamarind and boil for 25-30 mins until very soft.
Meanwhile, heat the oil in a frying pan and gently fry the shallots for 8-10 mins. When softened, add the spices, curry leaves, chillies and a good pinch of salt. Cook for another 2 mins, until fragrant.
Boil another pan of salted water and cook the beans for 4 mins until tender, then drain well.
Once the lentils are cooked, add the shallot spice mix and the beans, stir well and add more seasoning if necessary.