Preheat oven to 325 degrees. Line an 8x8 square dish with parchment paper or foil and spray lightly with cooking spray. Set aside.
In a large bowl, combine all ingredients for shortbread until moist. Press evenly into bottom of prepared pan. Set aside.
In a different large bowl, whisk together ingredients for pumpkin filling. Stir until smooth. Pour over shortbread and smooth the top. Sprinkle nuts and chocolate chips over top and press lightly into filling. Drizzle caramel sauce over top of entire dessert.
Bake 45 minutes to an hour or until pumpkin filling has set. Cool completely before removing. Cut into 16 equal squares and serve. (*I happened to put mine into the fridge and ate a piece cold and actually preferred it that way! So maybe give that a try to see if you'd like that better than warm or at room temperature.)