In a mixing bowl, combine the Greek yogurt, honey (or maple syrup), key lime juice, and lime zest. Stir until well blended and smooth.
Line a baking sheet with parchment paper. Pour the yogurt mixture onto the prepared baking sheet and spread it evenly to about 1/2 inch thick.
Sprinkle the crushed graham crackers evenly over the yogurt layer. If using, add the shredded coconut and chopped macadamia nuts on top.
Place the baking sheet in the freezer and freeze for at least 4 hours or until completely solid.
Once frozen, remove the yogurt bark from the freezer and let it sit at room temperature for about 5 minutes to soften slightly.
Break the bark into pieces and serve immediately or store in an airtight container in the freezer for up to 2 weeks.