Rinse urad daal thoroughly with water 2-3 times. Soak it in water for 4-6 hours.
Drain all the water out. Blend it to a smooth paste using a few spoons of water. Add green chilies and fresh ginger while grinding the soaked lentils. The consistency should be similar to that of thick cake batter, a easy test to check the consistency is to drop a little batter in the water and make sure it floats on the water. Add salt and lightly beat the batter with a hand blender to aerate it. This makes the vada's light and fluffy.
Heat the paniyaram pan on medium low heat. Add a few drops of oil in each round section and add 1 to 2 tablespoons of batter in each section. Cover the pan with a lid. Let it cook for 4-5 mins on low heat until the vada's are lightly golden on the bottom. Then slowly flip them over using a chopstick or spoon and cook the other side for another 3-4 mins.
Take a big bowl with 3 cups of water. Slowly remove the vadas from the pan and immerse them in the water. Continue making another batch of vadas while the first batch is soaking in the water.
In another bowl whisk yogurt, add ½ cup of water, salt and sugar and bring the yogurt to a smooth, pourable consistency. Take the vadas from the water one at a time and gently squeeze all the water by pressing them on the palm of your hands. Keep them in a serving platter.
Pour 1 cup of the prepared yogurt over the vadas. Continue cooking, dunking them in water, squeezing the water out, and pouring yogurt over them for the rest of the batter. The serving platter can then be refrigerated for up to a week or until you are ready to serve.
To serve this dish, take 3-4 vadas with some yogurt in a plate. Add a tablespoon of tamarind-date chutney. Sprinkle some red chili powder, ground cumin, and ground coriander. Spread a spoonful of the crunchy thin sev and garnish with cilantro. Cilantro and thin sev are optional but add a good texture and flavor to the dish.