Combine all chicken marinade ingredients. Place in a ziplock bag and marinate overnight or for several hours.
Combine all onion (or beef) marinade ingredients. Place one half in a ziploc bag and the other half in another ziploc bag. Marinate the onions in one bag, the beef in another overnight or for several hours. If you are not using beef, just make half the marinade.
Once you are ready to cook the meat, the chicken breasts can be grilled, baked, or pan fried until they reach an internal temperature of 165 degrees. The beef can be browned in a large skillet with the onions.
While the beef and/or chicken are cooking, make up the tzatziki sauce. Place the cucumber in a fine strainer, salt it abundantly and let it stand for 5 minutes. Squeeze all the excess water out of the cucumber.
Add the garlic and olive oil to a food processor and blend until it forms a smooth paste.
Place the cucumber, garlic paste, dill and yogurt in a big bowl along with some salt and pepper. Mix thoroughly. Set aside.
To assemble the gyros, place some beef or chicken, marinated onions on top of a homemade or store bought pita. Top with tzatziki sauce, tomatoes, and feta cheese if desired.
Notes
For a great Homemade pita recipe, visit Annie’s Eats: http://www.annies-eats.com/2008/08/10/pita-bread/