Preheat oven to 350°F (175°C) and grease a 9x13-inch baking dish or line with parchment.
In a large bowl, combine cake mix, pumpkin puree, eggs, oil, cinnamon, nutmeg, and salt. Beat until smooth.
Pour batter evenly into the prepared pan and smooth the top.
Mix chopped nuts, brown sugar, cinnamon, and melted butter in a small bowl; sprinkle evenly over the cake batter.
Bake 40–45 minutes, until a toothpick comes out mostly clean.
Cool completely before cutting; optional: chill for firmer slices.
Notes
Use pure pumpkin puree, not pumpkin pie filling.Toast nuts slightly for extra flavor.Evenly distribute the topping to prevent dry spots.Let cake cool fully for cleaner slices.