Preheat oven to 350° F (180° C). Spray a regular sized loaf pan with oil, or line the pan with parchment paper.
Toast the walnuts on a baking sheet for 10-12 minutes, if using. Remove from the oven once golden and set aside.
Combine the pumpkin, sugar, oil, molasses, and flax or chia egg in a medium-sized mixing bowl and stir well.
In a large bowl, combine the flour, baking soda, baking powder, salt, pumpkin pie spice, and cloves.
Add the wet mixture to the dry ingredients, and mix well.
Stir in the toasted nuts, if using.
Pour the batter into the pan and smooth out. Bake for 50-60 minutes or until an inserted toothpick comes out clean.
Allow to cool before removing from the pan.