Coat a 12 cup mini muffin pan with cooking spray. Divide popcorn, marshmallows and peanuts evenly among the cups.
Place the chocolate into a microwave-safe container. Heat on high for 45 seconds, then continue to heat at 15 second intervals, stirring each time, until chocolate is melted and smooth. Pour into the muffin cups, filling to the top. Gently tap the pan on the counter to release any bubbles. Refrigerate until chocolate is set. Unmould and enjoy!