Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish.
In a large bowl, combine the yellow cake mix, pumpkin puree, eggs, cinnamon, and nutmeg. Mix until smooth.
Pour the batter into the baking dish and bake for 30-35 minutes or until a toothpick comes out clean.
Allow the cake to cool slightly, then poke holes all over the top using a wooden spoon handle.
Pour sweetened condensed milk over the holes, letting it soak in thoroughly.
Spread whipped topping evenly on top and sprinkle with cinnamon if desired.