Using a serrated knife, cut cake horizontally into 2 layers. Place bottom cake layer, cut side up, on a serving platter. Mix frosting, cocoa powder, vanilla, and cinnamon in large bowl until combined. Spread about 1/4 of the frosting over top of cake layer on platter. Top with second cake layer, cut side down. Spread remaining frosting evenly over top and sides of cake to coat completely. Spoon apple pie filling into hole in center of cake. Place candles atop cake. Sprinkle top of cake with some corn nuts, pumpkin seeds, and popcorn. Sprinkle remaining corn nuts and pumpkin seeds around base of cake.