Wash, peel and boil the potatoes till tender. Drain the potatoes, and cut into small cubes. Set aside.
If using tamarind pulp, soak the tamarind pulp in hot water for about 15 – 20 minutes till soft. Mash the pulp with a spoon (or use your handto separate the pulp from the veins, seeds and membranes. Strain the tamarind pulp and set aside.
Heat oil in a small frying pan or small pot and add the cumin seeds.
Once the cumin seeds turn golden and release their aroma, add the boiled chickpeas and fry for about 3 minutes.
Add the red chili powder and salt, followed by the tamarind pulp and fry for 2 minutes. The chickpeas should be on the dry side.
Remove from heat and place the chickpea mixture in a medium sized bowl to cool.
Once the mixture has cooled down add the diced potato, tomato, onion and green chili. Mix together and garnish with chaat masala and green chilies.
Serve at room temperature.