For the pre-dough, mix 250 g wheat flour with 250 g water and 2 g yeast. Cover the bowl with cling film and let rise overnight at room temperature.
Mix the flours for the dough. Finely grate the zucchini. Add all ingredients, including the pre-dough, knead everything together well and cover the dough for 1 ½ hours.
Place the dough on the well-floured work surface and divide into two equal portions, shape each into loaves and cover and leave to rise for another 1 ½ hours.
Preheat the oven in time to 220 degrees. Cut into the loaves as desired, pour in well and bake for 30 to 35 minutes.