Preheat the oven to broil.
Add the oil to a skillet over medium heat, and cook the onions and peppers until softened.
Stir in the meat, and cook until browned. Drain the excess grease.
In a bowl, whisk together the cornstarch and chicken broth.
Add the worcestershire sauce, ketchup, taco seasoning and salt and pepper to taste to the meat mixture, and stir to combine.
Mix in the cornstarch mixture, and simmer until the mixture thickens.
Spoon the meat mixture into the buns, top with the cheese and broil for 1-2 minutes before serving.