Preheat oven to 250 degrees F (120 degrees C). Oil a 10x15 inch baking pan with sides.
Place popcorn and peanuts into a large, metal bowl, and set aside. Stir together the sugar, corn syrup, cocoa powder, and butter in a saucepan over medium-high heat until it comes to a boil. Boil for 2 minutes. Stir in the vanilla, then pour over the popcorn. Stir until the popcorn is well coated. Spread the popcorn into the prepared pan.
Bake in preheated oven for 30 minutes, stirring several times.
Remove from the oven, and allow to cool to room temperature. Break into small clumps, and store in an airtight container.