Preheat the oven and prepare the pan: Preheat your oven to 350°F (175°C) and grease or line a 9x5-inch loaf pan with parchment paper.
Grate and drain the zucchini: Grate the zucchini and squeeze out excess moisture using a kitchen towel or cheesecloth. Set aside.
Mix the wet ingredients: In a large mixing bowl, whisk together eggs, sugar, orange juice, and orange zest until smooth. Add the drained zucchini and mix to combine. Combine the dry ingredients: In a separate bowl, sift together flour, baking powder, baking soda, salt, and cinnamon (if using).
Mix the wet and dry ingredients: Gradually add the dry ingredients to the wet mixture, stirring until just combined. Avoid overmixing.
Fold in the cranberries: Gently fold the cranberries into the batter, distributing them evenly.
Bake: Pour the batter into the prepared loaf pan and bake for 55–60 minutes, or until a toothpick inserted into the center comes out clean.
Cool and slice: Let the bread cool in the pan for 10–15 minutes, then transfer it to a wire rack to cool completely before slicing.