Sprinkle evenly one finely chopped onion on a 9x13 casserole dish.
Gently pat 2 lbs ground beef over the onion. Press evenly making a giant hamburger patty.
Poke small holes in the meat. I use a straw.
Evenly sprinkle 1 tsp seasoned salt.
Bake at 400 for 20 minutes.
In a large baking dish, cut a large piece of aluminum foil and place in baking dish. (If you are using a casserole dish, you may need to 9x13 pans. If you are using a cookie sheet, you may squeeze them all in tightly in the aluminum foil.)
Place the bottom halves of 24 Hawaiian rolls on the aluminum foil.
Cut hamburger with a pizza cutter into 24 square patties. Place a hamburger patty on each roll.
Cut 12 slices of cheese into 4 quarters. Layer 2 squares of cheese over patties.
Place 2 pickles on each burger. Add ketchup and mustard to each patty.
Melt 4tbs butter.
In a small mixing bowl, add melted butter and 1 tsp Worcestershire sauce and 1 tsp mustard. Mix well. Brush butter mixture on top of Hawaiian rolls.
Cover sliders with aluminum foil and bake an additional 20 minutes or until cheese is melted. Serve.