• Line a large baking sheet with parchment paper and set it aside.

Make the Chocolate Bark

• Place the semisweet chocolate in a microwave-safe bowl. Microwave at 50% power for 1 minute. Stir, then continue to microwave at 50% power in 30-second intervals, stirring well after each interval, until completely melted and smooth.
• Stir the peanuts into the melted chocolate until well combined.
• Pour the chocolate mixture onto the prepared baking sheet. Use an offset or flexible spatula to spread it into an even rectangle, about 9- x 12-inches and no more than ¼-inch thick. Immediately scatter the Reese's Pieces evenly over the chocolate.

Make the Pumpkin Spice Drizzle

• Place the white chocolate in a small microwave-safe bowl. Microwave at 50% power for 1 minute. Stir, then continue at 50% power in 30-second intervals, stirring after each, just until melted and smooth. Stir in the pumpkin pie spice.

Decorate and Chill

• Using a small spoon, drizzle the pumpkin spice white chocolate over the bark. Immediately add the Halloween sprinkles and candy eyeballs, gently pressing the eyeballs into the chocolate if needed so they stay in place.
• Refrigerate for about 45 minutes, or until completely firm.

Break or Slice

• Once the bark is completely firm, break it into irregular pieces with your hands. If you prefer clean edges and more defined pieces, use a sharp knife to cut it into triangles or other shapes.