Preheat oven to 350°F (175°C). Grease a 9×5-inch loaf pan and line with parchment if you’re feeling fancy.

In a large bowl, whisk together flour, baking powder, baking soda, salt, and 1 teaspoon cinnamon. It’s a dry ingredients party—let them mingle.

In a separate bowl, beat eggs with sugar until light. Stir in oil and vanilla until glossy and smooth.

Fold in the grated zucchini just until combined. Don’t overmix; you’re not auditioning for a gluten-gluten-free finale.

Divide the batter in half. In one half, mix in the remaining cinnamon and brown sugar for the swirl. If you’re using nuts or chips, fold them into the main batter now.

Spread a thin layer of plain batter in the pan, then add a spoonful of cinnamon-swirl batter. Repeat to create ribbons as you layer. Marvel at your own decorative prowess.

Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean. If the top browns too fast, cover loosely with foil.

Cool in the pan for 10 minutes, then transfer to a wire rack. Slice when fully cooled for clean, easy cuts.