You'll notice there is no exemplary Greek kleftiko recipe, even when we were in Greece we got 3 different things in 3 different taverns in the same town. But at least, the recipe can be adjusted to tastes and likes and it will still have the Greek aromas, so it will still be delicious. The main rule for kleftiko is to use lamb, but... I've also tried combined with beef, pork, chicken. And there was another one with white cheese (telemea), but it didn't impress me much, I am going to experiment some more and I will let you know if I find anything of interest.
So, I'm going to show you a simple, unpretentious kleftiko recipe which you can adapt and switch the pork with the chicken, or the lamb with the pork/beef. I'd say that the only things that are obligatory are the potatoes, veggies and marinade. You can cook it in a deep Jena or ceramics baking dish, with a lid on - it's wonderful cooked this way, that's why I do it like this almost every time.
You can also bake the steak in the oven, wrapped in parchment paper, in individual pouches, and serve it like this. It will give a certain charm to it, it will be something out of the ordinary - but it's actually a simple steak with potatoes, packed with Greek flavours and served in an unconventional way.