Ingredients in Greek salads vary, but feta cheese and olives are essential.
Remove outer leaves of romaine, reserving for another use. Separate leaves from heart; arrange in a serving bowl.
Using a mandoline or a sharp knife, shave the onion and the cucumber into thin, transparent rounds.
Scatter onion, cucumber, and olives over romaine. Crumble feta directly onto salad. Drizzle with olive oil, season with salt and pepper; serve.