Wash, peel and grate the bottle gourd and keep it aside.
In a mixing bowl, add the rice flour, grated bottle gourd, cumin seeds, grated ginger, finely chopped green chilies, salt and coriander leaves and mix everything well.
Make a smooth dough without adding any water. Sprinkle water only if needed.
Heat oil over a medium flame.
Divide the dough into small round balls. keep them aside.
Grease a plastic sheet with little oil. Take a dough ball and flatten it into a thin round disc on the greased plastic sheet.
Make a small hole in the middle of the vada/dough disc and slowly drop it into the hot oil.
Deep fry them over a medium flame until golden brown on both sides.
Drain on a paper towel and serve hot with yogurt.
The oil should not be smoking hot. Fry the vadas over a medium flame. I have used the grated ginger and chopped chillies in this recipe, but you can use ginger green chilli paste. The oil should be hot enough to fry the vadas.