In a large wok / kadai, heat the oil.
Add asafoetida, immediately adding red chillies, mustard seeds, udad dal.
Once mustard seeds splutter and dal turns golden, add the chopped beans, salt - stir well and sprinkle water, cover and cook for 8-10 minutes on a low flame.
Check on the beans every 3 minutes or so, sprinkling some water, if it is too dry or catching at the bottom of the pan.
Once done (tender, but still retaining some crunch), sprinkle sambar powder, stir to mix well.
Remove from flame and garnish with coconut.
Serve with rasam-rice or sambar - rice.