In a skillet, cook the ground beef along with the chopped onion until the beef is browned and the onion is translucent.
In a separate bowl, combine the chili sauce, Worcestershire sauce, yellow mustard, brown sugar, salt, and pepper to create the sloppy joe sauce.
Add a small amount of water to the sauce to achieve a saucier consistency.
Take the hamburger buns and turn them inside out to prepare for grilling.
On the inside of the buns, layer a slice of cheese followed by a generous amount of the sloppy joe mixture.
Carefully flip the sandwich to cook it like a grilled cheese, grilling until the bread is golden brown and the cheese is melted.
