In a medium bowl, combine the Greek yogurt and mayonnaise until smooth.
Add the shredded chicken, walnuts, celery, red onion and currants to the bowl. Stir everything together until all the ingredients are well coated in the dressing.
For the best flavor, cover the bowl and refrigerate the mixture overnight to let the flavors meld.
To serve, spoon a generous portion of the chicken salad onto the bottom half of a potato roll, keeping the top half attached to create a pita-style sandwich.
Garnish with fresh dill if you like, and serve immediately. This also packs well for a picnic or a mid-day break.