Preheat oven (electric cooker: 200 °C/recirculating air: 175 °C/gas: see manufacturer). Peel onions and cut into strips. Heat a large pan without fat. Fry meat and onions for 5-8 minutes, turning them over.
Line baking tray with baking paper. Cut flat bread in half horizontally and place on the baking tray. First spread sauce, then meat on the bread. Rub Gouda directly over it. Crumble feta over it. Bake in a hot oven for about 15 minutes.
Clean, wash and shake dry the arugula. Serve pizza with rocket. Tsatsiki tastes good with it.