Prepare the Cake:

Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking dish.

Mix the Cake Batter: In a large bowl, combine the cake mix, pumpkin puree, eggs, vegetable oil, cinnamon, nutmeg, and salt. Mix until well combined and smooth.

Prepare the Cinnamon Swirl:

Mix Cinnamon Sugar: In a small bowl, mix together the brown sugar, ground cinnamon, and chopped nuts (if using).

Assemble the Cake:

Layer the Cake: Pour half of the pumpkin cake batter into the prepared baking dish. Sprinkle the cinnamon swirl mixture evenly over the batter. Pour the remaining batter on top, smoothing it out gently.

Create the Swirl: Using a knife or a skewer, gently swirl the batter to create a marbled effect, being careful not to mix it too much.

Bake:

Bake the Cake: Bake in the preheated oven for 45-50 minutes, or until a toothpick inserted into the center comes out clean.

Prepare the Glaze:

Make the Glaze: While the cake is baking, whisk together the powdered sugar, milk, and vanilla extract in a small bowl until smooth.

Serve:

Cool and Drizzle: Once the cake is done, allow it to cool in the pan for about 10 minutes. Drizzle the glaze over the warm cake before serving.