Preheat oven to 350°F (175°C). Grease a 9x13 inch baking dish.
In a large bowl, whisk together pumpkin, evaporated milk, eggs, sugar, cinnamon, ginger, nutmeg, and salt until smooth.
Pour mixture into the prepared baking dish.
Sprinkle 1 cup of the cake mix evenly over the pumpkin mixture.
Stir the remaining cake mix with melted butter until crumbly, then sprinkle over the top.
Top with chopped pecans if using.
Bake for 50–55 minutes or until the center is set and the top is golden brown.
Cool completely before cutting into squares.
Serve with whipped cream if desired.