Put the onion in a food processor until finely chopped Remove the onion from the processor and place in a towel Gather the sides of the towel and squeeze out the liquid from the onion In a mixing bowl place the onions, lamb, beef, and remaining ingredients and mix together well with your hands Cover the mixing bowl with Saran Wrap and place in the refrigerator for at least 2 hours to let the flavors mingle together Preheat oven to 325 degrees After the 2 hours take your meat from the mixing bowl and place into a food processor and process to until the mixture feels sticky( very well ground) Place the meat mixture into a 7x4 loaf pan and pack tightly no air pockets Place a damp towel into the bottom of a roasting pan and place the loaf pan on top of towel lined pan and place inside the oven Fill the roasting pan with boiling water half way up to the sides of the loaf pan Bake until the gyro meat has an internal temperature of 165 degrees and is no longer pink inside and the juices run clear Half way through the cooking process remove meat mixture from the pan and pour off excess fat return the meat back to the pan and continue cooking When the meat is done and slightly cooled cut very thin slices of meat and lightly brown on both sides inside a sauté pan Place meat slices in a nice warm pita wrap topped with tzatziki sauce , lettuce tomato and onion