Line a sheet tray with parchment paper and set aside.
Place the popcorn in a large bowl. Place the frosting in a microwave-safe bowl and heat for 30 seconds until it turns into a thick glaze.
Pour the frosting over the popcorn and gently fold together until all of the popcorn is evenly coated. Add 1 cup of the cake crumbs and gently fold. Turn the coated popcorn out onto the lined sheet tray and smooth out in a single layer. Sprinkle with the remaining cake crumbs. Let sit at room temperature until the frosting is set, about 30 minutes.