Prepare 9x13 pan. Line with foil and spray generously with nonstick.

In large bowl combine marshmallows and butter. Microwave on high until marshmallows fluff up to double their size (between 1-2 minutes depending on microwave). Remove from microwave and stir to combine marshmallows and butter.

Add popcorn and stir until mostly coated.

Add banana chips and walnuts. Stir to combine.

Gently fold the chocolate chunks in a little at a time to prevent it form melting too much.

Transfer mixture to prepared pan and press down firmly with hands or bottom of a cup.

Allow to cool. Remove from pan and carefully peel foil from bottom. Cut into 12 squares. Serve.