Heat the oven to 230.
Bake the washed and dried leeks on a nonstick sheet, without anything. Let them bake about 30 minutes. Check halfway through cooking that they are not burning.
Once cooked cut them lengthwise. At this point you can either remove the tender part, put it on a plate and season. Or leave the leeks whole, open, seasoned on a plate. You will still eat only the tender part; the outer leaf is tough and not very good.
Season generously with olive oil, fleur de sel , ground pepper and lots of fresh oregano.