Rinse the green moong dal thoroughly, then soak it in slightly warm water for 3 to 4 hours until softened. Drain the water completely and transfer the soaked dal to a blender along with ginger and garlic cloves. Grind it into a thick, smooth paste without adding any water to maintain its consistency.
Pour the blended mixture into a large mixing bowl. Add the grated bottle gourd, grated carrot, chopped green chilies, coriander leaves, turmeric powder, salt, garam masala, chaat masala, sugar, and oil. Mix everything well to combine. Stir in the semolina and gram flour, ensuring there are no lumps. Cover the bowl and allow the batter to rest for about 15 minutes to let the flavors meld and the texture develop.
Once rested, sprinkle eno fruit salt into the batter and gently mix it in one direction to keep it airy and light.
Heat a heavy-bottomed pan or kadai over medium flame and add oil for tempering. Once hot, add mustard seeds, sesame seeds, curry leaves, dry red chilies, and a pinch of hing. Let them splutter and release their aroma. Carefully pour the prepared handvo batter into the center of the kadai, spreading it evenly. Cover with a lid and cook over low to medium heat for 12 to 15 minutes until the base turns golden and crisp.
Using a spatula, gently flip the handvo to cook the other side. Cover again and cook for another 5 to 7 minutes, or until both sides are evenly browned and crispy. Repeat the process with the remaining batter if needed.
Once done, transfer the cooked handvo to a plate, let it rest briefly, then cut it into desired pieces. Serve warm with tangy green chutney or yogurt on the side for a wholesome and flavorful snack.