Preheat oven to 350 degrees F. Grease a 9x13-inch baking dish.
In a large bowl, whisk together the pumpkin, sweetened condensed milk, brown sugar, eggs, cinnamon, nutmeg, ginger and salt. Pour the pumpkin mixture into the prepared pan and spread into an even layer. Sprinkle the dry cake mixture evenly over the top of the pumpkin mixture. Pour the melted butter slowly and evenly all over the top of the cake mix. DO NOT MIX.
Bake for 40 minutes, then sprinkle the nuts over top (if using), and bake for an additional 20 minutes, or until the top is lightly browned and puffed. Allow to cool to room temperature before slicing and serving. Leftovers can be stored in an airtight container in the refrigerator for up to 3 days.