Peel the oranges and remove as much of the pith (white membrane) as possible.
Slice 4 of the oranges into thin rounds and place them in a shallow dish, slightly overlapping them.
Sprinkle the fennel strips, fennel leaves, (and olives if using) over the slices.
Squeeze the remaining oranges and place the juice in a small bowl. Whisk in the olive oil.
Drizzle the olive oil over, and sprinkle with salt and cracked pepper.
Cover tightly with plastic wrap and let the salad stand at room temperature for several hours. Every so often, tilt and turn the dish so that the oil and juices that have collected flow over and around the oranges.