Place the onion chunks in the food processor and blitz them until they are super finely chopped. Scrape into the center of a clean tea or flour sack towel, twist and squeeze it over the sink to remove any extra moisture.

Use your hands to combine them with the remaining gyro meat ingredients. Cover with plastic wrap and let the mixture rest for at least 1 hour but up to overnight in the refrigerator.

Preheat grill to high.

Place the meat onto the rotisserie skewer. Place a double-thick piece of aluminum foil folded into a tray directly under the meat to catch any drippings.

Cook on high for 15 minutes.

Decrease the heat to medium and continue to cook for another 20 to 30 minutes or until the internal temperature of the meat reaches 165°F.

Turn off the heat and allow to continue to spin for another 10 to 15 minutes or until the internal temperature reaches 175°F.

Slice and serve on pita bread with tzatziki sauce, chopped onion, tomatoes, and feta cheese.