1Peel the oranges and cut each one into 4 or 5 crosswise slices. Transfer them to a shallow serving dish and sprinkle them with the vinegar, olive oil, and oregano. Toss gently, cover, and refrigerate for 30 minutes.
2Toss the oranges again, arrange the sliced onion and black olives over them decoratively, sprinkle with chives and grind on fresh pepper.