Peel the oranges and split apart into segments. Cut into bite-sized pieces, removing any seeds. Place in a bowl and set aside.
In a pint-sized jar add the kefir, honey, and vanilla. Put the lid on the jar and shake it very well until combined. If the kefir is cold, the honey may clump at the bottom of the jar. Use a fork or a spoon to scrape it off the sides and bottom and cover and shake again until the honey dissolves.
Pour the dressing over the orange pieces, cover, and refrigerate at least 25 minutes to chill and allow flavors to meld. Sprinkle the chopped pistachios over top and serve.