Preheat the oven to 350 degrees F (175 degrees C). Grease a 10x15-inch baking pan.

Beat pumpkin, 2 cups white sugar, and oil in a mixing bowl; add eggs and mix well.

Combine flour, baking soda, cinnamon, and salt in another bowl; add to pumpkin mixture and beat until well blended. Pour batter into prepared baking pan.

Bake in the preheated oven until a toothpick inserted into the cake comes out clean, about 25 to 30 minutes. Set cake aside to cool.

Beat cream cheese, butter, and vanilla together in a mixing bowl until smooth. Gradually beat in confectioners’ sugar; add milk until frosting reaches desired spreading consistency.

Spread frosting evenly over cooled cake; sprinkle with walnuts.