In a large mixing bowl, start by combining your sliced onion, chopped potato, cauliflower, spinach, coriander, grated ginger, and green chilies. Add the gram flour, rice flour, baking soda, and all the powdered spices and cumin seeds.
Using your hands, mix everything together thoroughly. Squeeze the vegetables as you mix to help them release their natural moisture. This process, known as maceration, is key to creating a thick batter without adding too much water. If you have time, let the mixture rest for about 30 minutes to draw out even more moisture.
After mixing and resting, check the consistency. If the batter feels too dry and isn't clinging to the vegetables, add water one tablespoon at a time. You are aiming for a thick, clumpy batter that holds together, not a thin, runny one. Overwatering will lead to soggy pakoras.
Heat oil in a deep pan or kadai over a medium flame. To test if the oil is ready, drop a tiny bit of batter into it; it should sizzle and rise to the surface immediately. Using a spoon or your fingers, carefully drop small clumps of the batter into the hot oil. Don't overcrowd the pan.
Fry the pakoras for 4-5 minutes, flipping them occasionally, until they are deep golden brown and crispy on all sides. Use a slotted spoon to remove them from the oil and place them on a plate lined with a paper towel to absorb any excess oil. Serve them hot.