Preheat oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see manufacturer). Wash the tomatoes and cut them into thin slices. Cut mozzarella into approx. 16 thin slices. Halve the bread roll. Cover each half with tomatoes and mozzarella.
Bake in a preheated oven for 5-6 minutes.
Wash the arugula and shake dry. Put 1 slice of ham and some rocket on each half roll. Sprinkle with 1 tsp. pesto and serve immediately.