The key to achieving a good firm texture for the meat is to over-process the hell out of it and to add as little moisture as possible (hence squeezing the liquid out of the onion). If you have a food processor that is large enough to accommodate 2 1/2 lbs of meat, then use that. If not, a stand mixer will suffice...or be prepared to beat your meat into submission by hand and hate your life.
1 large onion, grated or pulverized in the food processor
2 1/2 lbs ground turkey
5 cloves of garlic, minced
1 tablespoon dried ground marjoram (you can use oregano in a pinch but it isn't as authentic-if you use oregano add some dried mint too)
1 tablespoon dried ground rosemary
1/2 teaspoon freshly ground black pepper
2 teaspoons salt
Lettuce, tomato, cucumber, spinach, red onion, alfalfa sprouts, green pepper, feta cheese or other accoutrements.
Preheat oven to 325 degrees. Grate the onion and put in a colander lined with paper towels or cheesecloth (cheesecloth works better for this). Squeeze the juice out of the onion and return to the food processor or deposit in a mixing bowl. Add remaining ingredients and mix for several minutes or until meat has achieved a "silky" texture and seasonings are well incorporated. Wet hands liberally (ground turkey tends to be sticky) and shape meat into a loaf and place in a large, ungreased baking dish. Bake until internal temperature registers 170 degrees, about 1 1/2 hours at high altitude (let your thermometer be your gauge). Let meat sit for at least 10 minutes before cutting into it. After meat has rested, slice-or shave it very thinly with a very sharp knife. Serve in a pita with tzatziki and your favorite vegetables.
Note: Your hands are going to stink like onion after this. To get rid of the smell, rub your hands with something stainless steel under running water.
Low carb without the pita.
Adapted from Alton Brown Gyro recipe for lamb gyros as well as several others floating around on the web.