In a medium size mixing bowl, soak urad dal in plenty of water for 4~6 hours or overnight.
Drain dal and grind the soaked dal with little water into a smooth paste. Add water 1 tablespoon at a time. Batter should hold its shape when held in your hand.
Add cumin seeds, chopped green chilies, curry leaves, salt and cabbage (if using). Mix well.
Whisk the batter for about 5~7 minutes to add air into it. This step helps in making fluffy vada instead of dense ones.
Heat oil for frying in a small wok on medium~medium-high heat.
To make vada, place a bowl of water and wet both your hands. Take about ¼ cup of batter and place it on your palm. Flatten it lightly and poke a hole in the middle with your finger.
You can also use a ziploc bag or aluminum foil to make vada. Moisten it with water, place the batter on it, flatten it and poke a hole in the middle.
Slowly transfer the vada into the hot oil and fry until golden brown and cooked through, about 3 minutes per side. Depending on the size of your pan, you can make 3~4 vada at a time.
Carefully remove them from the oil using a slotted spoon. Place them on a paper towel lined plate and repeat with the remaining batter.
Serve immediately with ginger chutney or sambar or coconut chutney or anything else.