* Slice the oranges and arrange them in a serving plate.
* Clean the fennels, removing the base, the outer tough leaves, and the green stems.
* Slice the fennel very thin. Transfer to a bowl.
* Dress the fennel with extra-virgin olive oil, salt, and pepper.
* Transfer the fennel to the serving dish. Drizzle with extra-virgin olive oil. Add olives and onion if desired.