Preheat the oven to 350°F (175°C).
Grease a 9x5 inch loaf pan.
In a large bowl, combine pumpkin puree, oil, sugar, and eggs; mix well.
In another bowl, whisk together flour, baking soda, baking powder, cinnamon, nutmeg, and salt.
Gradually add the dry ingredients to the pumpkin mixture, stirring until just combined.
If using, fold in the chopped walnuts.
Pour the batter into the prepared loaf pan.
Bake for 60 minutes or until a toothpick inserted comes out clean.
Allow to cool in the pan for 10 minutes before transferring to a wire rack.
Slice and enjoy your delicious pumpkin bread!