In a medium bowl, mix Greek yogurt, key lime juice, protein powder, lime zest, powdered sweetener, and vanilla extract until smooth.
Line a baking sheet with parchment paper or a silicone baking mat and spread the yogurt mixture evenly in a thin, uniform layer.
Sprinkle crushed graham crackers, toasted coconut, and extra lime zest evenly over the yogurt layer.
Freeze the baking sheet for 2 to 3 hours until the yogurt bark is fully frozen and set.
Remove the bark from the freezer, lift the parchment, and break it into pieces.
Enjoy immediately or store in an airtight container in the freezer up to 2 weeks, separated by parchment to prevent sticking.