First make the green chutney paste. Place all the paste ingredients into a blender and blitz to form a smooth paste. Remove from the blender and set aside. In the same blender , grind the garlic and ginger with a splash of water. Set aside.
Heat the oil in a heavy based saucepan over a medium heat. Add the onions and fry for 10-12 minutes until they begin to brown. Add the garlic and ginger paste and fry for a minute.
Add the green chillies and chicken and fry for 2-3 minutes. Season and add the water then reduce the heat to low and simmer for 15 minutes, stirring halfway through.
Add the green chutney paste, most of the diced mango, the sugar and the lime juice and simmer for 10 minutes, stirring often, Add the remaining mango and serve warm with rice.