Pour 2/3 cup water into water reservoir and cover it. Assemble processing bowl and steaming basket with slicing disc.
Slice mango into steaming basket. Remove lid and slicing disc, then replace lid.
Steam until light turns off.
Remove steaming basket. Reserve steaming liquid from processing bowl for pureeing. Insert puree/chopping blade and place mango and banana in bowl. Puree, adding enough reserved liquid to reach desired consistency. Cool before serving.
Stir in yogurt.
Refrigerate remaining mixture or freeze in storage containers.