Step 1: Combine crushed shortbread cookies, ¼ cup chopped pecans, and melted butter in a medium bowl. Press the mixture firmly into the bottom of a 9x13 inch baking dish. Refrigerate for at least 30 minutes while preparing the fillings.
Step 2: In a large mixing bowl, beat softened cream cheese and powdered sugar with an electric mixer until light and fluffy. Gently fold in half (about 4 ounces) of the thawed whipped topping until just combined. Spread this mixture evenly over the chilled crust.
Step 3: In another large bowl, whisk together the instant vanilla pudding mix and cold milk for about 2 minutes, until it begins to thicken. Stir in the pumpkin puree and pumpkin pie spice until well combined. Spread this pumpkin mixture over the cream cheese layer.
Step 4: Carefully spread the remaining whipped topping over the pumpkin layer, smoothing it out. Sprinkle the remaining ¼ cup chopped pecans over the top for garnish.
Step 5: Refrigerate the pumpkin delight for at least 4 hours, or preferably overnight, to allow all layers to set and flavors to meld. Serve chilled and enjoy this amazing pumpkin delight!