Actually, I can't believe I haven't posted this before, one of my very favorite sandwiches. There's nothing to it, that's probably why, and probably because you make some form of this for yourself anyhow. But in case not, and in case you love Greek/Middle Eastern flavors, here's a quick, filling, bursting-with-flavor sandwich, somewhere between a grilled cheese and a pizza.
I start with pita bread or naan (not pocket bread-style, although it would work, it's just not as chewy and soft as the thicker loaf style; I buy whole-wheat naan at the deli at Whole Foods, there's a white version in the bakery at Byerly's). I use half a loaf, but you could easily prepare one as a whole for two people. I give the bread a spritz of oilve oil spray on both sides, then set it in a medium-hot skillet - while it toasts on one side, I halve a handful of cherry tomatoes, chop a handful of spinach, and halve a few kalamata olives. I flip the bread, crumble a bit of feta cheese over it, sprinkle with Greek seasoning (or salt and pepper), then top with the tomatoes, spinach, and olives. When the bottom is toasted I slide it onto a plate and drizzle with tsatsiki (I use nonfat Greek yogurt, grate in some cucumber and onion, some minced dill if you have it, stir in a little salt - I make a cup or so at a time; extra keeps tasty in the fridge for a few days).
Sit down with a knife and fork and be ready for the flavor explosion of a gyro or falafel sandwich, with far (far!) fewer calories. Enjoy!