If you have precooked meat on hand, you can make gyros sandwiches at home in the time it takes to set the table. Any kind of thinly sliced, precooked meat will work, whether you buy it at a grocery deli, use leftovers from a restaurant meal or precook it yourself. Make sure to use Greek rather than pocket pita. Greek pita is soft and fluffy, and easily absorbs the extra juices from the meat and yogurt.
Heating in the Oven
If the meat you're using is thinly sliced, it will take about five minutes to heat in a 375-degree Fahrenheit oven. Preheat the oven while you're assembling the other ingredients. Arrange the gyros meat on a baking dish or piece of foil. Bake it until it's heated through. You can heat the pita bread in the oven at the same time, but give the meat a few minutes' head start.
Heating in the Microwave
It will take seconds to reheat precooked gyros meat in the microwave. Prepare and assemble all the other gyro ingredients before heating the meat so it will be optimally hot when you assemble your sandwich. Spread the thin meat in a single layer and microwave it for 20 to 30 seconds, depending on the thickness. Assemble your gyros soon after you take the meat out of the microwave.
Heating on the Stovetop
Reheat precooked gyros meat on the stovetop using a skillet, or a saucepan if you're not heating much. Use a thin layer of oil in the pan, enough to keep it from sticking but not enough to make it greasy. If you're using an oil with a low smoke point, such as olive oil, cook it gently for a longer time. If you're using a high heat oil such as peanut oil, you can cook it hotter and faster. If you don't have the other gyros components assembled, the meat will stay warm in the pan for a few minutes while you get them ready.
Assembling the Sandwiches
Heat your meat and pita as soon as possible before you assemble your gyros. You can heat the bread either in the oven or in a lightly oiled pan. Be sure not to overcook it if you're using the oven because it can grow dry and brittle. Spread a thin layer of tsatsiki sauce on the pita and then layer the meat, greens, tomato and onion, then drizzle on extra sauce.