In a large skillet, heat medium-high and brown the ground beef until no longer pink, about 6-8 minutes. Add the diced onion and minced garlic, cooking until softened, approximately 3-4 minutes. Drain excess fat, then stir in Worcestershire sauce, salt, and pepper. Let it simmer for 5 minutes before setting aside.

Preheat your oven to 350°F (175°C). Tear hamburger buns into bite-sized pieces, place them in a mixing bowl. Drizzle with melted butter, stirring to coat evenly. Spread the buns onto a baking sheet and toast in the oven for about 10-12 minutes until golden and crispy.

In a medium bowl, combine mayonnaise, ketchup, sweet pickle relish, yellow mustard, white vinegar, sugar, paprika, garlic powder, and onion powder. Mix thoroughly, tasting to adjust any seasonings before setting aside.

Grease a 9x13-inch baking dish generously. Layer the cooked beef mixture evenly, followed by slices of American cheese and pickles. Drizzle half of the special sauce on top, layer the toasted buns over everything, and finish with shredded cheddar cheese.

Transfer the casserole into your preheated oven, baking uncovered for 20 minutes. Look for bubbling edges and a lightly golden top before removing it.

Allow the casserole to cool for about 5 minutes before slicing. Top with shredded lettuce, additional pickles, and remaining special sauce before serving.