In a small saucepan over medium heat, stir together the peanut butter, maple syrup, and coconut oil until melted and smooth.
Remove from heat and stir in the vanilla, pumpkin puree, hemp hearts, and pumpkin pie spice until combined.
In a large bowl, add the crisp rice cereal. Pour the wet mixture over top and mix until fully combined.
Pour into an 8x8-inch baking dish lined with parchment paper. Press down firmly (very firmly!!) and evenly with a spatula.
Optional: melt white chocolate chips in the microwave in 30-second increments, stirring between each, until smooth. Drizzle or pipe over the top. For Halloween season, I like to pipe into a spider web!
Freeze for 15-20 minutes until just firm. Lift out using the parchment, cut into squares, then transfer to the fridge for another 1-2 hours.