Start by lining a 9x13 inch baking dish with parchment paper. This will prevent the bars from sticking and make it easy to lift them out later. Set aside.
In a medium saucepan, melt the salted butter over low heat. Once melted, add the marshmallows and stir continuously until they are completely melted and smooth.
Remove the saucepan from heat and stir in the Peter Pan Simply Ground peanut butter until fully combined.
In a large mixing bowl, add the plain popcorn. Pour the melted marshmallow and peanut butter mixture over the popcorn, and use a spatula to gently fold everything together until the popcorn is evenly coated.
Transfer the popcorn mixture to the prepared baking dish. Use the spatula to press it down firmly into an even layer.
In a microwave-safe bowl, melt the semisweet chocolate chips in 30-second intervals, stirring in between until smooth. Once melted, drizzle the chocolate over the pressed popcorn mixture.
Let the popcorn bars cool at room temperature for about 30 minutes, or until the chocolate is set.
Once set, lift the bars out of the baking dish using the parchment paper. Cut into squares or rectangles and serve.