Mix flour, yeast and 1/2 teaspoon salt. Add 125 ml lukewarm water and knead to a smooth dough with the dough hooks of the hand mixer. Cover and leave to rise in a warm place for about 30 minutes. Wash, clean and dice the tomatoes. Peel onions and cut into rings.
Heat the oil in a small pan. Briefly sauté the onion rings in it and take them out. Mix tomatoes, onions, capers and herbs, season with salt and pepper. Knead the dough again and divide it into 6 equally sized pieces. Roll out to a flat cake (approx. 12 cm Ø). Place on a baking tray lined with baking paper. Spread the tomato mixture on top. Drain the tuna, pluck into pieces and spread on the pizzas. Add cheese in small stains.
Place on a baking tray lined with baking paper. Spread the tomato mixture on top. Drain the tuna, pluck into pieces and spread on the pizzas. Add cheese in small stains. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 15-20 minutes. Arrange on a plate, garnish with marjoram
15 minutes waiting time