Place a large nonstick or cast iron skillet over medium-high heat.
Coat the pan with oil, and add the ground beef.
Stir for 3-5 minutes until the beef is mostly browned. Strain out most of the fat that accumulates.
Add in the onions and bell peppers, and stir for 2-3 minutes until the onions are translucent.
Add in the beef broth followed by the ketchup, Worchester sauce, salt and pepper.
Mix cornstarch with a tablespoon of water in a cup, and add to the pan, stirring constantly as it will start thickening quickly.
Within a few minutes, the mixture should be thick enough to start forming mounds.
Remove from heat, add cheese and slowly stir it in. Meanwhile, start toasting the buns.
Once cheese is fully melted, spoon onto buns. Serve immediately and enjoy!