Drain the mozzarella and cut into slices. Clean, wash and slice the zucchini and tomatoes. Put them in an ovenproof dish or pan. Peel garlic and press it through a garlic press.
Wash the basil, dab dry and chop finely, except for one leaf for garnishing. Mix garlic, basil and oil. Spread over the vegetables and season with salt and pepper. Bake in the preheated oven (electric: 200° C / gas: level 3) for 25 to 30 minutes.
Dice the mortadella and pour over the vegetables halfway through cooking. Serve garnished with basil.