01 - Set oven temperature to 350°F and allow to fully preheat.
02 - In a large skillet over medium-high heat, cook ground beef and chopped onion, breaking up the meat while stirring, until beef is fully browned and onion becomes translucent, about 5 to 7 minutes. Drain excess fat.
03 - Pour in sloppy joe sauce, stirring to combine. Let simmer over medium heat for 2 to 3 minutes, just until thoroughly heated and mixture thickens slightly.
04 - Arrange the slider bun bottoms in a baking dish. Evenly distribute the beef mixture onto each bun. Top each portion with half a slice of cheddar cheese, then cap with slider bun tops.
05 - Place baking dish in preheated oven and bake uncovered for 5 to 7 minutes, until cheese is fully melted and buns are lightly toasted.
06 - Remove sliders from oven and serve immediately while warm.