Briefly blanch (scald) spinach leaves in salted water, rinse with ice cold water and drain. Cut mozzarella into small cubes. Finely chop onion and garlic clove. Cut the cap off four particularly nice tomatoes and hollow them out so that they can still stand up afterwards. Dip the remaining tomatoes briefly in boiling water, peel off the skin, remove the stem and seeds and cut the flesh into cubes. Sauté the onion and garlic in a little hot olive oil until translucent. Roughly chop the olives, cut the well squeezed spinach a few times and add both. Season with salt and pepper. Mix in tomato and mozzarella cubes, stir well and season again. Remove from heat and fill the hollowed tomatoes with the mixture. Sprinkle with breadcrumbs and parsley and drizzle with olive oil. Place in an ovenproof dish and bake in a preheated oven at 180 °C for about 10 minutes. Arrange one stuffed tomato on each plate. Be careful when cutting the tomatoes – they are very hot inside!