In small bowl combine the salt, oregano, pepper, cumin, cayenne and cinnamon and mix thoroughly.
In large bowl combine meat, onions and spice mix. Add garlic and vegetable oil, mix thoroughly with hands until spices are evenly distributed. Refrigerate covered several hours.
In a small skillet, fry a small amount of the meat mixture in a little butter. Taste for seasoning and adjust, if desired. Blanch bacon by simmering in hot water about 3 minutes. Drain on paper towels. Line loaf pan (8 1/2 x 5 x 3") with bacon covering sides and bottom.
Pack gyros meat into pan, filling to the top of the pan. Cover with remaining slices of bacon
Place filled pan in hot water bath, reaching 3/4 of the way up the loaf pan. Bake at 375°F for 20-30 minutes. Reduce heat to 325°F and continue baking 30 minutes longer.
Remove pan from oven. Remove loaf pan from hot water bath and place on wire rack to cool.
Cover with aluminum foil and weigh down with about 2 lbs. weight to compress loaf. Cool to room temperature, refrigerate meat, covered with weight 12 hours or overnight to ripen and increase flavor. Meat will keep for up to 4 days refrigerated.
Slice very thin and serve in pita bread with sliced onions, tomatoes and tzatziki sauce.