Combine sourdough starter, water, and oil in a mixing bowl. In a separate bowl combine flour, yeast, sugar, and salt. Combine the liquid ingredients into the dry ingredients. Then mix in the chopped rosemary and lemon zest into the bread, folding and kneading the bread until well incorporated.
Place the dough in a bowl and cover with plastic wrap. Keep covered until the dough has double in size, about 90 minutes.
Gently divide the dough into half and shape each piece into a round loaf. Place each loan on a parchment-lined baking sheet. Cover the dough again and allow them to rise for about an hour. Towards the end of the hour, preheat the oven to 425 degrees. Spray the loaves with lukewarm water and make at least two fairly deep slashes in the bread. Be creative if you want!
Take the loaves from about 25 to 30 minutes until the loaves are a deep golden brown.