In a bowl, mix together the coconut, pistachios and raisins until well combined.
Using a small, sharp knife, slice a deep pocket horizontally in the bread disks. Stuff each bread pocket with the nut and raisin mixture.
In a bowl, whisk together the yogurt, sugar, and pinch of salt until smooth and well combined, adding more sugar and salt to taste if necessary.
Heat the oil in a small pan over a medium heat. Add the mustard seeds and cook for 20 to 30 seconds, or until they start to pop. Caution: Keep the pan well away from your eyes and face. Be careful of the popping mustard seeds and splattering oil.
Add the dried chiles and curry leaves, and continue to cook for 20 to 30 seconds. Add the yogurt mixture, and stir well, until the mixture is well combined.
Place the stuffed bread disks into a large mixing bowl and pour the yogurt mixture over them. Give the bowl a shake to ensure that the yogurt mixture coats the bread disks, including the underside. Set the bowl aside for 30 minutes to soak, and then serve.
*Can be found at specialty Asian markets.