Seriously, you actually put lettuce on your pizza? I'd love to see a pic of the finished product. I can't imagine that worked out very well.
When I make a Greek pizza, I do it like this: The sauce is olive oil with minced fresh garlic and greek oregano sprinkled on top. Then a layer of 50/50 mozzarella and feta (I really like Valbreso French Feta). The toppings are fresh tomatoes, sliced red onion, and Kalamato olives (rinsed, pitted, & sliced), plus another sprinkling of greek oregano. Maybe some bell peppers could go on as well.
Some people use butter instead of olive oil for the base, but I really don't know why. I also have no idea why some pizza places put ham on a greek pizza. Squid or greek chicken or anything remotely mediterranean would make more sense to me.
I guess my response doesn't really answer the question about putting a Greek salad on a pizza. So my answer is that I just use the parts of the salad that seem to work on a pizza. Like I've never tried to put cucumbers on my Greek pizza, because I don't think they would taste good cooked. And, just so you know, Greek salad doesn't have to have lettuce. Without lettuce, it's called Horiatiki Salata, which means villager's salad.