Line a baking sheet* with parchment paper. Set aside.

In a medium bowl, stir the zest of one lemon into the Greek yogurt. Spoon the yogurt mixture onto the prepared baking sheet and with a spatula spread it evenly to the edges; it should be about ½-inch thick.

Evenly sprinkle the yogurt with the grapes and pistachios, and then dust the remaining lemon zest over the yogurt.

Place the baking sheet in the freezer for at least 4 hours or until the yogurt sets. Gently break the yogurt bark into 24 pieces. Store in a re-sealable container in the freezer for up to 2 weeks.