Wash and soak the Urad dal for at least 2-3 hours or soak it for overnight.
Drain the soaked dal and then blend or grind it in a blender (grinder) till smooth fluffy paste.
Do not use too much water, when grinding, just sprinkle little water for easy grinding.
Add chopped onion, green chili, chopped ginger, chopped curry leaves, chopped coriander leaves, salt and mix well.
Heat oil in a kadhai or deep pan. Now wet your hand lightly in water, take a small portion of mixture in your hand.
Make a whole in center with you thumb, then upturn your hand and drop Vada in the hot oil.
Deep fry Vada till all side golden brown. Use same process for remaining batter or mixture.
Drain Vada on observant paper, Medu vada is ready to serve with coconut chutney and sambhar.