Preheat the oven to 350°F (175°C). Grease and flour a baking pan.

In a mixing bowl, whisk together the dry ingredients: flour, baking powder, baking soda, cinnamon, nutmeg, and salt.

In another bowl, mix the granulated sugar, brown sugar, and oil until well combined. Add the eggs one at a time, mixing well after each addition.

Stir in the grated carrots and crushed pineapple.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Fold in the chopped walnuts if using.

Pour the batter into the prepared baking pan and spread evenly.

Bake in the preheated oven for 25-30 minutes or until a toothpick inserted in the center comes out clean.

Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.