1Prepare vegetables: Slice potato and onion into thin, even rounds. Slit green chili lengthwise, leaving the stem intact.
2In a large bowl, combine gram flour, rice flour, turmeric powder, red chili powder, asafoetida, cumin seeds, carom seeds, baking soda, and salt.
3Gradually add water to the dry ingredients, whisking continuously to form a smooth, thick batter without lumps. The batter should be thick enough to coat the vegetables evenly.