Make spread. In a small bowl, stir together the mayonnaise, minced garlic, and crumbled bacon. Set aside.
Cut bread and spread top with bacon mayo. Using a serrated knife, slice the French bread in half horizontally. Using a spatula, evenly spread the mayonnaise mixture over the top slice of the French bread loaf.
Layer meat and cheese. Using the bottom half of the French bread, start layering the sandwich by placing evenly across the bread the ham, turkey, salami, and cheese.
Add toppings. Next, place the sliced tomatoes over the meat and cheese. Separate the rings of the onion and spread across the desired amount to use. Top the tomatoes and onion with shredded lettuce. Sprinkle the oregano, salt, and pepper over the lettuce.
Assemble and cut. Place the dressed top half of the French bread over the sandwich. Cut the sandwich into 6-8 servings, depending on how thick you want the slices to be. Serve immediately or wrap in plastic and refrigerate for use later the same day. For a nice presentation, you can use sandwich toothpicks pierced with olives placed into individual slices.