Add popcorn kernels to a Stasher bag, or similar silicone bag. Seal bag, leaving about 1 inch open to release steam. You can use a brown paper bag too. Roll it up, and place rolled portion on the bottom.
While chocolate is in microwave, spray popcorn with cooking spray, sprinkle kosher salt over popcorn. Seal and shake in bag. Taste and repeat if needed.
Pour about ⅓-1/2 of popcorn into serving bowl. Drizzle ⅓-1/2 chocolate over popcorn, then sprinkle about ⅓-1/2 of m&ms over popcorn. Repeat until all popcorn is in serving bowl.