Wash the zucchini and rub dry. Drain the olives. Cut zucchini, olives and feta cheese into thin slices. Wash fish fillet, dab dry, sprinkle with lemon juice, season with salt and pepper. Alternately cover with zucchini, olives and cheese. Strip rosemary needles from the branch and spread on the fillet. Cook in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 15-20 minutes