Soak the lentils overnight (optional)
Peel and dice the potatoes into equal-sized pieces and put in a saucepan with just enough water to cover the potatoes till cooked through.
Once they're cooked, discard the water, mash the potatoes until there are no lumps, and season them with salt and black pepper.
Strain the soaked lentils, discard the water, and add the lentils to a saucepan. Chop the ½ onion and add it to the lentils.
Add the ginger, and garlic paste, red chili powder, coriander powder, salt, and 1 cup of water and bring to a boil.
Reduce the heat to medium, and cook till there is only 1 inch of water left.
Cover the saucepan with foil and steam the lentils for 10 minutes on the lowest heat setting till they are cooked through.
Once done, place the lentil mixture in a food processor, and pulse till it's mashed.
Mix the mashed lentils and potatoes next, and add the amchur powder and 1 teaspoon of the chaat masala at this point.
Once you have a uniform mixture, start shaping your patties, using water to help you seal any cracks.
Beat the eggs in a shallow dish.
Heat the oil in a large, wide frying pan.
Once the oil is well heated, dip the patties in the egg mixture and shallow fry on medium heat till they're light brown on each side
Slice the buns and place them on the pan to heat (see notes).
Assemble the bun kebabs with the patties, two chutneys, sliced onions, and whatever else you wish to add.