In a large skillet over medium heat, add ground beef and cook while breaking apart until no longer pink. Drain grease.
1 pound ground beef
Add onions, green peppers, and mushrooms to the skillet. Cook for an additional 5 to 7 minutes, or until onions are tender.
1 small yellow onion, diced, 1 small green bell pepper, diced, 1 cup sliced mushrooms
In a small separate bowl, combine beef broth and cornstarch. Whisk until no lumps remain. Pour broth over meat and stir well.
1 cup beef broth, 1 Tablespoon cornstarch
Add ketchup, Worcestershire sauce, salt, and pepper. Stir well. Let cook until most of the liquid has been absorbed, about 5 minutes.
2 Tablespoons ketchup, 1 Tablespoon Worcestershire sauce, ½ teaspoon salt, ½ teaspoon ground black pepper
Turn off the heat and add cheese to top of the beef. Stir slightly to melt.
1 cup shredded mozzarella cheese
Serve meat and cheese mixture on sesame seed hamburger buns.
6 sesame seed bakery hamburger buns