Place the garlic cloves in a food processor and pulse until very finely chopped.
Add onion and puree until smooth.
Add ground beef with all of the spices. Pulse until the mixture becomes like a paste. Scrape down the sides of the bowl in between pulses.
Place the mixture in a loaf pan. Compact it as much as possible.
Bake for 45 minutes to 1 hour or until the internal temperature registers 165 °F.
Allow the pan to cool at room temperature completely. Refrigerate at least 2 hours before removing it from the pan.
Remove from pan onto a cutting board. Using a sharp serrated knife, slice it thinly. Pour all of the pan juices over the slices along with any of the fat that has gelatinized. It adds so much flavor when heating it up for the sandwiches.
At this point, the gyro slices can be placed in a freezer-safe bag and frozen for future use.
To make the Gyro sandwiches, place a cast iron pan over medium heat and cook the gyro slices until they are browned on both sides.
Warm the pita bread slightly. Place some chopped lettuce, onion, and tomato slices over the pita, the warm gyro slices, and tzatziki sauce with crumbled feta. Serve immediately. Enjoy it!
