Preheat oven to 220 °C. Brush baking dish with 2 tablespoons olive oil. Drain tuna well in a colander, divide into small pieces with a fork.
Cut toast slices into cubes. Pit olives and cut in half. Roughly chop parsley leaves. Put the above ingredients in a bowl, mix gently with salt, pepper, lemon juice and 2 tablespoons of olive oil.
Cut out the stalk from the tomatoes. Cut the tomatoes into slices about 1 cm thick, place them in the baking dish and season with salt and pepper.
Spread tuna mixture on tomatoes, sprinkle with Parmesan and rosemary needles, drizzle with 2 tablespoons olive oil and bake tomatoes in preheated oven (middle shelf) for about 10 minutes.