Preheat your oven to 350°F (175°C) and grease a standard loaf pan.

In a large bowl, whisk together flour, baking soda, baking powder, salt, cinnamon, and sugar until blended.

In another bowl, whisk the eggs with oil and grated zucchini until smooth.

Gradually fold the dry ingredients into the wet mixture until just combined.

Prepare the cinnamon swirl by mixing sugar and cinnamon. Layer half of the batter, sprinkle half of the swirl, add the rest of the batter, then finish with the remaining swirl.

Bake in the preheated oven for 55 to 65 minutes. Check doneness with a toothpick.

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