In a medium bowl, combine the graham cracker crumbs and melted unsalted butter, mixing until the mixture resembles wet sand. Press this mixture firmly into the bottom of a greased 9x13-inch pan to form a solid crust. Ensure it's even and well-packed, then place it in the refrigerator for about 30 minutes to chill and set.

While the crust sets, beat the softened cream cheese in a large mixing bowl with an electric mixer until creamy and smooth. Gradually blend in the powdered sugar until thoroughly combined. Gently fold in 1 cup of whipped topping until fluffy and no lumps remain. Carefully spread this mixture evenly over the chilled crust, smoothing it out to the edges with a spatula.

In a separate bowl, whisk together the pumpkin puree, vanilla pudding mix, cold milk, and pumpkin pie spice until the mixture thickens and is well blended, about 2 minutes. Carefully spread the pumpkin mixture over the cream cheese layer, ensuring it covers the surface evenly.

Top the pumpkin layer with the remaining whipped topping, using a spatula to spread it smoothly across the entire surface. Make sure to reach the edges for a nice finish.

Sprinkle mini chocolate chips and chopped pecans over the whipped topping layer, distributing them evenly for a charming presentation.

Refrigerate the completed Pumpkin Lush for at least 4 hours or ideally overnight, allowing the flavors to meld together and ensuring the dessert is well-chilled.