What ingredients do you use in Greek salad?
Which ingredient would you never use?

There is only one horiatiki. It is tomato, cucumber, onions, black olives with a piece of feta cheese on top, with oregano and olive oil.
You do not put lettuce in the Greek salad. It is not horiatiki with lettuce.   
Yorgos Lesiotis, taverna owner

I use tomato (peeled), onion (thinly sliced, dunked in ice water for a minute just before adding to salad), feta, olives, olive oil, a dash of vinegar, fresh oregano, cracked black pepper. The tomato goes in first with the oil and vinegar and is left to macerate for a while, not unlike strawberries in alcohol.
I'm sure there are many ingredients used in Greek salad that are ridiculous, given today's modern twists–freeze-dried feta, ouzo gelee, and the like–but one I would never use (and this is just a matter of taste, and, I realize, totally contrary to tradition), is green pepper. Absolutely no place in a Greek salad, or anywhere else, for that matter.
Stefanos Potamianos, writer and foodie

People would often ask me why do you stack the salad? Well here’s the reason. My thought process was to take something as well known as the “Greek Salad” and make it contemporary and still paying homage to my heritage. Well, one day while researching different types of feta that are made in the many regions of Greece, there it was a photo of a Corinthian column in one of the feta pictures, this became the model for what would become my signature stacked Horiatiki salad topped with fresh oregano leaves mimicking the Corinthian column.
I never put lettuce in my Horiatiki (Greek Village Salad).
Paul Delios, culinary director, At the Greek Table