Isn't *every* salad served in Greece technically a Greek salad? So happy to read about your adventures!
I seem to remember that most salads in Greece did not include lettuce. Lots of good stuff but no lettuce. While the “Greek Salad” in the US typically has an abundance of lettuce plus feta cheese dressing.
Lettuce in salads probably depends on the time of year and how much is imported. It being a cool weather crop is unlikely to survive the Greek summer temperatures. Quite possibly their food is locally grown by tradition and by economic reasons.
They have wonderful lettuce here, but they deploy it in other salads. The kind of salad that is predominantly tomatoes, olives, onions, peppers, fennel and feta is referred to here as a Greek salad, too.