Heat a large skillet over medium heat. Add the beef and cook, breaking up any big chunks, until no pink remains, about 5-6 minutes.
Season with salt and pepper. Stir in the big mac sauce and 1 slice of American cheese until melty and well combined.
Meanwhile, brush the melted butter on the insides of four buns. Broil for 3-4 minutes, or until golden brown.
Top each bottom bun with additional big mac sauce, shredded lettuce, diced onion, pickle chips, and a slice of cheese. Scoop beef mixture over top, top with the second bun, and dive in!