Add ground beef, salt, pepper and Worcestershire sauce to a large bowl. With your hands, gently mix it all together.
Divide the ground beef mixture into 2oz portions. Do not compress the burgers into defined patties, these should still be slightly loose with rough edges.
Heat the oil in a large cast iron skillet over medium-high heat. Place 4 small handfuls of sliced onions onto the skillet in 4 separate piles. Place one portion of ground beef on top of each onion pile. With the back of a heavy duty spatula, press the burgers down and allow them to sizzle a bit before removing the spatula. Continue with the remaining burgers. Allow patties to cook for about 2 minutes, then with the spatula, flip them over and allow to cook on the other side for an additional 2-3 minutes. Top each with ½ of a slice of cheese in the last 30 seconds. Remove cooked patties and continue with remaining 4 patty portions.
Divide the Hawaiian slider buns in half. Place lettuce, tomato, pickles and a dollop of Stonewall Kitchen Country Mayup on the bottom half of each bun. Top with a cooked burger patty and then the top portion of the bun. Serve hot.