Place red onion and garlic in the blender/food processor and blend until finely chopped but not liquified.
Add all of the seasonings and the meat. Depending on your processor size you may have to do this in batches. Blend until it is a smooth cohesive sticky texture. I place in a bowl after and mix by hand even more to ensure flavor consistency.
Place in a tin foil bread pan and evenly spread it out. Bake for 60 minutes or until the internal temperature reaches 160℉. I also like to make sure the outside has a good crisp on it.
Drain of all the fat and let rest until you can handle the loaf of meat. (~30 min)
Using your LEM meat slicer on a very thin setting, slice your gyro meat. If you do not have a meat slicer, this can be accomplished by cutting thin slices with a sharp knife.