Soak the urad dal for atleast 4 hours or overnight.
Drain the soaked dal and grind it to a smooth batter with no or very little water if required. If the batter becomes water, you can add semolina to the batter.
Add cumin seeds, black pepper, curry leaves, green chillies, ginger, coconut and salt into the batter. Stir and mix well by hand for 3-4 minutes to make the batter light and fluffy.
Heat sufficient oil in a deep heavy bottom pan to fry the vadas. The temperature of the oil should neither be too hot nor too cold. When you drop a little batter into the oil, it should rise and float on the surface.
Take a bowl of water and wet your palm. Take some batter in your wet palm and make a hole in the center using your thumb like a doughnut.
Invert your palm and slide the vada into the oil. Deep fry on low medium flame till they turn light brown or golden in color. Slightly increase the heat to medium high two minutes before taking out the vadas from the pan. This will make the vadas crispy from outside and soft inside.
Drain the excess oil by placing the vadas on kitchen paper towel or any absorbent material. Serve the medu vadas hot or warm with sambhar and coconut chutney.