Peel the mango and slice the flesh away from the stone, catching the juice. Add the fruit flesh to the juice and blend to a puree with 2 tbsp water and the lemon juice.
Push through a sieve and stir in the sugar, cinnamon and coriander. Transfer the mixture to an ice cream maker and churn for 15 - 20 minutes. (Alternatively transfer to a shallow metal dish and put in the freezer for about 3 hours, stirring vigorously every 30 minutes to prevent large ice crystals from forming. )
Peel the oranges with a sharp knife, removing all the white pith. Then separate the segments by cutting down inside the segment skins. Mix the orange segments with the orange liqueur.
Arrange the orange segments on 2 plates. Place scoops of mango sorbet on each. Garnish with mint leaves and dust with icing sugar.