Heat the oil in a saucepan.
Add the onions and saute until translucent, about five minutes on medium heat.
Grind together the ginger, garlic, green chilies and the coriander and cumin powders into a fairly smooth paste.
Add the paste to the onions and saute until the mixture is rather dry and does not smell raw, about 5 minutes.
Add the beans and turmeric. Add salt to taste and a cup of water and bring to a boil. If the curry gets too dry at any time, add more water, a little at a time.
Simmer on low heat about 5 minutes.
Add the coconut milk, jaggery and lemon juice and heat through.
Turn off the heat and garnish with coriander leaves.
Serve hot with rice.