Heat orange zest, juices, sugar and ginger and simmer until a thin syrup consistency. Remove from heat and cool. In a blender, purée canteloupe with cooled syrup until smooth. Add yoghurt, 1/2cup sour cream and vanilla and purée until smooth. Chill for at least 4 hours before serving.
For garnish, stir remaining ¼ cup sour cream with honey and mint. Dollop or swirl sweetened sour cream on soup before serving.