Step 1: Preheat your oven to 350°F (175°C). Line a 9x5 inch loaf pan with parchment paper, leaving an overhang on the longer sides to help lift the bread out later.
Step 2: In a large bowl, whisk together the all-purpose flour, 1 cup granulated sugar, baking powder, 1 teaspoon ground cinnamon, nutmeg, cloves, and salt. Set aside.
Step 3: In a separate medium bowl, combine the eggs, vegetable oil, Greek yogurt, and vanilla extract. Whisk until smooth.
Step 4: Add the wet ingredients to the dry ingredients. Stir gently with a spatula until just combined. Do not overmix; a few streaks of flour are fine. Fold in the shredded zucchini.
Step 5: In a small bowl, mix together the ¼ cup granulated sugar and 1 tablespoon ground cinnamon for the swirl.
Step 6: Pour half of the zucchini bread batter into the prepared loaf pan. Sprinkle half of the cinnamon swirl mixture evenly over the batter.
Step 7: Carefully spoon the remaining batter over the cinnamon sugar layer, spreading it gently to cover. Sprinkle the remaining cinnamon swirl mixture on top.
Step 8: Using a butter knife or a skewer, gently swirl the cinnamon sugar into the batter with a few passes, creating a marbled effect. Be careful not to overmix.
Step 9: Bake for 60-65 minutes, or until a wooden skewer or toothpick inserted into the center of the loaf comes out clean with no wet batter. A few moist crumbs are acceptable.
Step 10: Let the bread cool in the loaf pan on a wire rack for 10-15 minutes before carefully lifting it out using the parchment paper overhang. Transfer to the wire rack to cool completely before slicing and serving.