Put the fresh tamarind pulp into a cup with a few tablespoons of water and set aside for about 30 minutes.
Drain the potatoes, chop them into small 1 cm cubes and then put them into a large mixing bowl and add the drained chickpeas.
Coarsely chop the onion and add that in along with the chopped coriander.
Chop the tomatoes in quarters and add them in.
Chop the mango into cubes and add it in.
Slice the coconut into 1 cm or so strips and add them in.
The tamarind should now be soft and squishy. Strain it through a sieve to remove the stones and fleshy pith and then pour it into the bowl.
Mix all the ingredients in the bowl together and then season to your taste with the salt and chilli.
Spoon the mixture onto a plate and then sprinkle over some of the amchur if you have it.