Puree the mango in your food processor until smooth.
Pour into a saucepan, and stit in the chickpea flour, yogurt, water, ginger, and chillies.
Bring them slowly to the boil, stirring occasionally. Simmer for 4 - 5 minutes until thickened slightly, then set aside off the heat.
Heat the oil in a frying pan over medium heat. Add the mustard seeds and cook for a few seconds until they begin to pop, then add the cumin seeds.
Add the curry leaves and cook for 5 minutes. Stir the spice mixture into the soup, return soup to the heat and cook for 10 minutes.
Press through a sieve, (if you like) then season to taste.
Leave the soup to cool completely, then chill for at least 1 hour.
Ladle the soup into bowls, and top each with a dollop of yogurt. Garnish with shredded mint leaves and enjoy.