Put the flour in a bowl. Crumble yeast into it. Add sugar, salt, oil and 150 ml lukewarm water. Knead to a smooth dough with the dough hooks of the hand mixer. Cover and leave to rise in a warm place for 30 minutes.
Knead again and cut in half. Roll out on a floured work surface to two round bases (approx. 20 cm Ø). Place on a baking tray lined with baking paper, spread with pieces of tomato and pre-bake in a preheated oven (electric cooker: 200 °C/ gas: level 3) for approx. 15 minutes. In the meantime, peel onion and cut into rings. Drain the tuna and pluck it roughly. Grate cheese. Cover pizzas with tuna, onion and olives. Season with salt, pepper and marjoram. Sprinkle cheese on top.
Drain the tuna and pluck it roughly. Grate cheese. Cover pizzas with tuna, onion and olives. Season with salt, pepper and marjoram. Sprinkle cheese on top. Bake for another 10 minutes