How to Make It
Preheat oven to 350°F. Place walnuts, maple syrup, water, pumpkin, salt, and 1 tablespoon of the pumpkin pie spice in an Instant Pot. Set pot to Sauté, and cook, stirring often, for 10 minutes.
Place lid on Instant Pot, and lock it. Set pot to High Pressure. Set vent to Sealing, and cook for 10 minutes. After 10 minutes, carefully release the pressure valve, and carefully remove lid.
While walnuts cook, line a rimmed baking sheet with parchment paper, and lightly spray with cooking spray. Set aside.
Spread cooked walnut mixture in a single layer on prepared baking sheet. Bake in preheated oven for 15 minutes, stirring every 5 minutes to cook evenly. Toss together warm nuts, sugar, and remaining 1/2 tablespoon pumpkin pie spice in a large bowl until coated evenly. Pour back onto baking sheet to cool completely, about 10 minutes. (Nuts will not completely crisp in the oven, but will crisp upon cooling.)