Cut off the orange caps at the top and bottom, then peel the thick-walled peel from top to bottom. Now cut the peeled oranges into thin slices and place them on a large plate. Pour the orange juice that comes out when peeling / cutting over the orange slices. Cut the onion into wafer-thin rings, spread over the oranges.
Clean the fennel bulb, cut into small cubes and mix with olive oil, white wine vinegar, salt and pepper in a small bowl. Possibly some squeezed orange juice to make the dressing milder.
Pour the marinade over the orange slices. Chop the rosemary and fennel greens and sprinkle with them on the salad. It is best to marinate about 30 minutes before consumption, because the marinade has to soak in a little.