Coat a large nonstick skillet with cooking spray and heat over medium-high. Add the beef and salt. Reserve 1 tbsp of the yellow onion and add the remaining yellow onion to the skillet. Cook, breaking up the meat with a wooden spoon, until the beef is cooked through and no longer pink, 7 to 9 minutes. Let cool. Set aside.
Meanwhile, place 1½ cups of lettuce each in 4 medium bowls. Top each bowl with a quarter of the tomato, 3 pickle slices, 2 tbsp cheese, and the red onion (if using).
In a small bowl, stir the ketchup, mayonnaise, mustard, Worcestershire sauce, and reserved 1 tbsp yellow onion. Finely chop the remaining 3 dill pickle slices and add to the bowl.
Divide the beef mixture among the bowls of lettuce. Serve with the special sauce.