Season. In a large bowl, mix the ground beef with the salt, pepper, onion, garlic, and Worcestershire sauce.
Shape. Form the hamburger into four 8 oz patties. (Make them about a ½ inch bigger in circumference than the hamburger buns, they will shrink while cooking.)
Cook. Heat a cast iron skillet over medium-high heat until very hot and lightly smoking. Add as many burger patties as you can to the pan without them touching. (you may have to cook them in batches) Cook for 3-4 minutes, flip the patties and add 2 slices of cheese to each and cook for another 3-4 minutes. Transfer the cooked hamburgers to a plate and rest for 2-3 minutes.
Assemble. To build the hamburgers, first spread a thin layer of thousand island dressing on the buns. Place 2-3 leaves of lettuce on the bottom bun, add 1 slice of tomato, top with the burger patties, add 2 tablespoons of the caramelized onions on top, and place on the top bun. Serve immediately.