This is one of my favorite ways to use up leftovers. I throw a loaf of bread in the bread maker, prep the leftovers and we have a great lunch or dinner with little extra work.
For the filling you can use just about anything. I had some leftover beef stew so I used that. I have also made this with pot roast, leftover thanksgiving turkey and gravy, chicken curry and most soups. I especially love German Lentil soup in them. With soups just strain the broth off and use the rest as the filling. I you want you can even thicken some of the broth for a sauce to bind it all together. If you start from scratch another thing we like to stuff them with is chopped chicken tossed with a little alfredo sauce.
If I am using something that has a really chunky filling, like stew or roast, I chop it up into fairly small pieces.
Roll the dough out so that it is large and thin. Using a pizza cutter or sharp knife cut the dough into 4 in squares. Top with some of whatever filling you choose to use. Fold over and press the edges to seal. Brush with butter and sprinkle with the garlic, oregano, and grated cheese. Bake at 350 for 20 - 30 minutes until the bread looks cooked and browned on top. These make great lunches as well.