Heat oil in a pan and add mustard seeds. Once they crackle, toss in cumin seeds, asafetida, chopped green chili, and ginger garlic paste. Fry everything for a minute.
Next, sprinkle red chili powder, turmeric powder, coriander powder, and dry mango powder. Fry the masala quickly on medium-low flame, making sure it does not burn.
Now, add the boiled potatoes and mix them well with the masala. Season with salt and fold in fresh coriander leaves. The stuffing is ready.
In a separate bowl, combine gram flour, corn flour, ginger garlic paste, red chili powder, turmeric powder, salt, baking soda, and coriander leaves. Mix all the dry ingredients well.
Gradually pour in water, stirring continuously to make a smooth batter. Ensure the batter is neither too thick nor too thin and free of lumps.
Take two slices of bread; spread green chutney on one and tamarind chutney on the other. Spread the prepared stuffing evenly on one slice, then cover with the other slice like a sandwich. Cut diagonally.
Dip each bread sandwich into the batter, coating it well on all sides.
Finally, deep fry on medium flame until both sides turn golden brown and crispy.