Preheat the oven to 350°F (175°C).

Combine the yellow cake mix, vegetable oil, eggs, sour cream, canned pumpkin, and pumpkin pie spice in a large bowl. Mix until the batter is smooth and well blended, about 2-3 minutes.

Layer half of the batter into a greased baking pan, spreading it evenly.

Mix the brown sugar, chopped walnuts, and a sprinkle of pumpkin pie spice in a separate bowl. Spread this mixture over the first layer of batter.

Pour the remaining batter over the filling layer. Swirl gently with a knife to create a marbled effect.

Bake in the preheated oven for 40 minutes or until a toothpick comes out clean when inserted in the center.

Cool the cake before drizzling with a glaze made from powdered sugar, milk, and vanilla.