Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking pan.
In a large bowl, mix pumpkin puree, evaporated milk, eggs, sugar, cinnamon, nutmeg, allspice, and salt. Transfer mixture to the prepared pan. Pour dry yellow cake mix over the mixture, sprinkle with walnuts, and drizzle with melted margarine.
Bake 35 minutes in the preheated oven. Reduce heat to 325 degrees F (165 degrees C), and continue baking 15 minutes, until a toothpick inserted in the center of the cake comes out clean.
