Scrub the mango, peel and cut into cubes. Retain the mango seed; that too can be added to the chaatni.
Cook for a few minutes letting the mango cubes take a golden hue.
(Optional) In a small pan, roast the fenugreek and fennel seeds till fragrant. Cool and grind into a powder. Sprinkle the powder on the chaatni.
Serve the chaatni cool or cold, at the end of the meal or before the dessert.