Heat oven to 350 degrees. Spray a 9x13 baking dish with cooking spray.
In large mixing bowl, combine the pumpkin, evaporated milk, brown sugar, eggs, and pumpkin pie spice. Whisk together until combined and smooth. Pour into the baking dish.
Sprinkle the dry cake mix (do not prepare) evenly over the top of the pumpkin mixture. Sprinkle chopped pecans evenly over the cake mix.
Drizzle the melted butter evenly over the top of the pecans. Try and cover all the dry cake mix, that way you don't end up with dry cake mix spots once it's baked.
Bake for 45-50 minutes. The edges will be golden brown and the center will be set.
Let sit for about 20 minutes (so it's not piping hot) and serve warm with vanilla ice cream or whipped cream.