Filo pastry (you can make your own, gawdhelpyou, or buy the frozen sort.)
Feta, one parcel
You have to muck about with the spinach because as I stated, it is the dampest vegetable. Put it in a bowl, salt lightly, and then squeeeeeeze all the water out. You end up with interestingly green water- save this for a stew or something.
Lightly fry the onion and leek (chopped, obvs.) I don't cook the garlic at this stage, but if you want a more subtle garlicness then fry it as well.
Crumble the feta. Mix it with the egg, spinach, vegetables, and lemon juice.
Prepare the pastry by brushing each layer with oil, on an oiled baking tray. Place filling on pastry and encase it somehow.
There are a few ways to do this; the Greek one looks more regular and like a big flat pie, or you can wrap it into individual neat little triangles. Balkan-style is rolled up. How you do it won't really affect the taste, so go nuts.
Cook until the pastry is obviously done. If you un-dampened the spinach right then the filling will be solid and it won't collapse, but if it does it's still really really nice. Just chaotic.