Halve the passion fruit and scoop the pips and pulp into a strainer placed over a bowl. Press the pips with the back of a spoon to extract all the juice and then discard the pips.
Squeeze the juice from the oranges and pour into a food processor or blender with the passion fruit juice.
Add 1 scoop of mango sorbet and blend briefly to combine. Pour into a glass, add the second scoop of sorbet, and serve immediately.