Boil the potato pieces in a pan of salted water for 15 to 20 minutes, or until tender. Drain well, and mash with a potato masher or ricer until smooth. Set aside to cool. In a bowl, gradually add enough water to the chappati flour to be able to bring the mixture together as a dough. Bring the mixture together into a ball using your hands, then turn out the dough ball onto a lightly-floured work surface and knead lightly for 3 to 4 minutes, or until the dough is smooth and elastic. Set aside.
In a large bowl, mix together the cooled mashed potatoes, and the ground coriander, ground cumin, amchoor powder, chopped green chile, chopped cilantro, lime juice, and chile powder until well combined. Season the mixture with salt, to taste. Divide the potato mixture into 6 even portions, and roll each portion into a ball, using your hands, and set aside.
Roll 6 egg-sized balls from the dough mixture, and then flatten them into 4-inch disks using your hands or a lightly-floured rolling pin. Place 1 potato ball on top of each dough disk, then bring the dough around the potato balls and seal the edges, using a little water, if necessary.
Carefully flatten the stuffed dough balls slightly using your hands.
Heat a griddle pan or tawa (Indian griddle) over a low heat. Brush each of the stuffed dough balls all over with the oil, and cook for 3 to 4 minutes on each side, or until golden brown on both sides. Serve immediately.