Peel the oranges thickly all around, also removing the white skin. Collect the juice in a small bowl.
Cut the oranges into 0.5 cm thin slices, remove any existing slices. Spread the orange slices out on a large plate.
Clean the fennel bulb and remove the hard outer parts. Put the fennel greens to one side for garnishing. Cut the tender fennel heart into small cubes.
Cut the onions into very fine rings.
For the dressing, whisk the orange juice with the balsamic vinegar and olive oil. Finely chop the rosemary and mix in. Season to taste with salt and pepper.
Toss the fennel cubes thoroughly in the sauce, remove and spread over the orange slices.
Spread the onion rings and black olives over the orange platter. Drizzle the rest of the dressing over the salad. Grind the pepper coarsely and garnish with the fennel greens.