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 2 oz 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 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 aioli on the bottom half of each bun. Top with a cooked burger patty and then the top portion of the bun. Serve hot.