Heat the oil in a large nonstick skillet over medium high. Add the onion and peppers; sauté 3 minutes until tender. Add in the beef and continue to cook, breaking it up and browning, for another 3 minutes.
Stir in the ketchup, Worcestershire, taco seasoning, salt, and pepper.
Add the flour and cook for about 1 min. Stir in the broth; simmer for about 3 minutes, stirring occasionally, until mixture thickens slightly. Add the shredded cheese to the skillet and mix. Serve on buns with a slice of cheese.