Spray an 8 inch square glass pan with cooking spray.
Microwave the butter for about 30 seconds, until melted. Add in the marshmallows and for about 1 min. 30 seconds, stirring every 30 seconds. Stir mixture until the marshmallows are melted and smooth.
Mix the sunflower seeds and Cheerios into the melted marshmallow/butter mixture. Stir until blended, and then press into the pan.
Melt the chocolate chips in a zip lock bag in the microwave. Cut off a corner of the bag and drizzle the chocolate over the bars. Let sit for 1 hour so the chocolate can harden.