Slice the yellow onions into thick half-inch rounds. Marinate with Worcestershire sauce, a drizzle of olive oil, Tony Chachere's seasoning, and brown sugar for 15 minutes.

Heat a skillet over medium-low heat and cook the marinated onion rounds for about 10 minutes on each side until golden brown.

Season ground beef in a mixing bowl and divide into four portions, shaping into thin patties approximately ¼ inch thick.

Heat olive oil in a skillet over medium-high heat, sear patties for 2-3 minutes, flip, and add a slice of cheese on each patty for the last minute.

Combine mayonnaise, relish, Dijon mustard, garlic powder, onion powder, smoked paprika, and cayenne pepper in a bowl to create the special sauce.

Assemble the burger by placing a caramelized onion slice as the base, topping with a beef patty and special sauce, add another onion slice on top.