Preheat oven to 350°F (175°C) and grease a 9x13-inch baking dish.
In a large mixing bowl, whisk together pumpkin puree, evaporated milk, eggs, sugar, and cinnamon until smooth.
Pour the pumpkin mixture evenly into the prepared baking dish.
Sprinkle the dry yellow cake mix evenly over the pumpkin layer.
Top with chopped pecans.
Drizzle melted butter evenly over the entire surface.
Bake for 50-55 minutes, or until the top is golden brown and set.
Cool slightly before serving. Top with whipped cream if desired.