In a large skillet over medium heat, add the ground beef and diced onion. Cook, breaking up the meat with a wooden spoon, until the beef is browned and the onion is tender, about 5-7 minutes. Drain off excess grease.
Stir in the dill pickle relish, ketchup, yellow mustard, Worcestershire sauce, garlic powder, onion powder, and salt and pepper. Mix well and cook for another 5-7 minutes until heated through and flavors meld together.
While the mixture is simmering, toast the hamburger buns lightly on a separate skillet or under a broiler if desired.
To assemble the Sloppy Joes, place a generous scoop of the beef mixture onto the bottom half of each bun.
Top each sandwich with shredded lettuce, a sprinkle of cheddar cheese, and a drizzle of Thousand Island dressing. Cover with the top half of the bun.
Serve immediately while hot and enjoy!