Stone and peel the mango.
Transfer the mango to a food processor or blender and process to a purée.
Put the yogurt and agave nectar, according to taste, in a large bowl, scrape in the seeds from the vanilla pod and beat together. Gently fold in the mango purée and spoon into tall glasses.
Scoop the seeds from the passion fruit and spoon over the smoothie. Serve immediately with thin biscuits, if liked.