In a large mixing bowl, mix rice and all lentils. Rinse, drain, and soak them in enough water for approximately 5-6 hours.
Transfer the soaked mixture into a blender jar and blend until a smooth batter forms.
Return the batter to the mixing bowl and add yogurt, thoroughly mixing everything using a spatula or your hands.
Cover the bowl and place it in a warm spot to ferment for about 5-6 hours.
Once the batter has fermented, add grated Lauki, carrot, coriander leaves, and ginger-chili paste.
Add turmeric, red chili powder, sugar, salt, and baking soda, mixing until everything is well incorporated.
Heat oil in a kadhai or frying pan. Once the oil is sufficiently hot, add mustard seeds, sesame seeds, hing, and curry leaves.
Carefully pour approximately 2 cups of the batter over the tempering. Reduce the flame to medium-low, cover, and allow it to cook for about 8-10 minutes.
When the bottom part turns a delightful golden brown, flip the handvo upside down. Using a flat spatula, start from the edges, cover it again, and cook for an additional 5-7 minutes.
Your Handvo is now ready. Transfer it to a serving plate, cut it into pieces, and serve it alongside some chutney and a hot cup of chai.