Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners or grease it with cooking spray.

In a large mixing bowl, combine the pumpkin puree, vegetable oil, granulated sugar, brown sugar, eggs, and vanilla extract. Mix until smooth.

In a separate bowl, whisk together the all-purpose flour, baking soda, baking powder, salt, and pumpkin pie spice.

Gradually add the dry ingredients to the pumpkin mixture, stirring until just combined. Do not overmix.

If desired, fold in the chopped walnuts or pecans and chocolate chips.

Divide the batter evenly among the prepared muffin cups, filling each about two-thirds full.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted in the center comes out clean.

Remove the muffins from the oven and allow them to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.