Heat 2 tb ghee in a skillet over low heat. Saute the onion, asafetida, mustard seeds & ginger until the onion is golden brown. Stir in garam masala, green mango powder, salt & cayenne. Mix thoroughly.
Add beans, cover the pan & cook over moderate heat for 10 minutes until the beans are tender. Stir in cilantro & remove from heat.
Divide into 8 portions.
Brush one half moon of pastry with water & fold into a cone. Fill each cone with 1 portion of filling & seal the top. Repeat with remaining pastry.
Heat enough ghee in a wok or large skillet to deep-fry 4 samosas at once. When very hot, deep-fry the samosas for a few minutes until golden-brown on both sides. Remove from heat & drain well before serving.