In a mixing bowl, combine the peanut butter, Greek yogurt, honey, and vanilla extract. Stir until the mixture is smooth and well combined.
If desired, fold in the mini chocolate chips and chopped nuts for added texture and flavor.
Line an 8x8-inch baking dish with parchment paper, leaving some overhang for easy removal.
Pour the peanut butter yogurt mixture into the prepared baking dish and spread it evenly.
Cover the dish with plastic wrap and freeze for at least 4 hours, or until firm.
Once frozen, lift the bars out of the dish using the parchment paper overhang. Cut into squares or rectangles.
Store any leftovers in an airtight container in the freezer for up to 2 weeks.