In a large skillet over medium heat, cook the ground beef for 5-7 minutes until browned. Add onions and garlic, cooking for another 3 minutes.

Preheat oven to 350°F (175°C). Tear hamburger buns into pieces in a bowl, drizzle with melted butter, and toast in the oven for 5 minutes.

In a bowl, combine mayonnaise, ketchup, sweet pickle relish, yellow mustard, white vinegar, sugar, paprika, garlic powder, and onion powder. Whisk until smooth.

Grease a baking dish and layer half the beef mixture, 4 slices of cheese, chopped pickles, onions, followed by a third of the special sauce and toasted bun mixture.

Bake the casserole at 350°F (175°C) for 20 minutes until cheese is melted and bubbly.

Let cool for 5 minutes, then garnish with lettuce, extra pickles, onions, and drizzle remaining special sauce over the top.