To make the pickled red onions, simply slice them about 1/8-inch thick, and cover with red wine vinegar for a few hours, or overnight. They will turn into the beautifully colored garnish for these gyros.
I like to serve the fried slices on flat bread that's been spread with tzatziki. Top with some shredded lettuce and chopped cherry tomatoes. Layer on the meat slices and top with pickled red onions.
Get the recipe for Tzatziki Sauce.