In a mixing bowl, combine the Greek yogurt, honey, and vanilla extract. 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 out evenly to about 1/2 inch thick.
Scatter the mixed berries, chopped nuts, and chia seeds (if using) evenly over the yogurt layer. Press them gently into the yogurt.
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 baking sheet and break it into pieces.
Serve immediately or store in an airtight container in the freezer for up to 2 weeks.