Preheat oven to 200 degrees. Put popcorn in a large bowl. Add the nuts; set aside. Put sugar, corn syrup, butter, cocoa, and salt in a medium saucepan. Cook over medium heat, stirring, until mixture comes to a gentle simmer, about 5 minutes.
Pour sugar mixture over popcorn and nuts; toss to coat. Transfer to rimmed baking sheets; bake, stirring every 20 minutes, until almost dry, about 1 hour. Let cool on sheets on wire racks.