In a large mixing bowl, combine warm water, yeast, and sugar. Stir gently and let sit for 5 to 10 minutes until the mixture is foamy.
Add the olive oil, egg, salt, and ground cinnamon to the yeast mixture. Stir to combine.
Gradually add the flour, about 1 cup at a time, mixing well after each addition until a soft dough forms.
Turn the dough onto a lightly floured surface and knead for about 8 minutes until smooth and elastic. Add a little flour if the dough is too sticky.
Place the dough in a lightly oiled bowl, cover with a clean kitchen towel, and let it rise in a warm place for about 1 hour or until doubled in size.
After the dough has risen, gently punch it down and fold in the grated zucchini and chopped walnuts (if using) until evenly distributed.
Shape the dough into a loaf and place it into a greased 9×5 inch loaf pan. Cover with the towel and let rise for another 30 minutes until it has risen slightly above the edge of the pan.
Preheat the oven to 350°F (175°C).
Bake the bread for 25 to 30 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
Remove the bread from the oven and let it cool in the pan for 10 minutes. Then transfer it to a wire rack to cool completely before slicing.