Lower the flame and splutter the mustard seeds, add the hing, curry leaves, chillies. Stir once.
If using onions add them and stir fry till translucent.
Add the French beans, salt, coconut. Mix well.
Cover with a lid that is filled with water. Cook covered on low flame till the steam escapes from the sides of the lid.
Switch off the gas and let the vegetable sit for 4-5 minutes.
Serve hot with chapatti, and or rice and daal.
Notes
In case your French beans are not tender add a tablespoon or 2 of hot water in the pan.
Keep an eye on the French beans they should cook just right and not become brown or even crisp. In case you are not sure remove the cover and stir in between. Add water if needed.