1. Soak the urad dal and moong dal in water for 4-5 hours. Drain the water and grind the dals to a fine paste in a blender or food processor. Add water as required.

2. Add cumin seeds, black pepper, ginger paste, and salt to the dal paste. Mix well.

3. Heat oil in a deep frying pan over medium heat.

4. Wet your hands and take a small amount of the dal mixture. Roll it into a small ball and flatten it slightly.

5. Gently slide the vadas into the hot oil and fry until golden brown.

6. Remove the vadas using a slotted spoon and place them on a plate lined with paper towels to drain excess oil.

7. Soak the fried vadas in warm water for 10-15 minutes.

8. Squeeze out the water from the vadas and arrange them on a serving dish.

9. Whisk the yoghurt and add salt, cumin powder, chaat masala, red chilli powder, and roasted cumin seeds. Mix well.

10. Pour the yoghurt mixture over the vadas.

11. Garnish with chopped coriander leaves and sprinkle some red chilli powder on top.

12. Refrigerate for 1-2 hours before serving to allow the vadas to absorb the yoghurt sauce.

Note: You can also add sweet tamarind chutney or green coriander chutney to the dahi vada as per your preference.