Preheat the oven to 300°F. Line a large baking sheet with parchment paper.
Add the pretzels to a large bowl.
In a small bowl, whisk together the melted butter, brown sugar, and pumpkin pie spice until well combined.
Pour the mixture over the pretzels and toss until evenly coated.
Spread the pretzels in a single layer on the prepared baking sheet.
Bake for 12 to 15 minutes, stirring halfway through, until the coating looks slightly dry and set.
Let the pretzels cool completely on the baking sheet. The coating will continue to firm up as they cool.