Best Philly Cheesesteak Sloppy Joes

1 tablespoon olive oil
1 pound lean ground beef
1 small onion, finely diced
1 green pepper, diced
4 cloves garlic, minced
1 cup reduced sodium beef broth
1 tablespoon cornstarch
1 ½ teaspoons beef bouillon
2 tablespoons ketchup
2 tablespoons Worcestershire sauce
1 teaspoon Dijon mustard
1 tsp EACH dried oregano, dried parsley
½ tsp EACH salt, pepper, dried basil, paprika
¼ teaspoon red pepper flakes, more or less to taste
3/4 cup freshly grated sharp cheddar cheese
BUNS
6 brioche hamburger buns
softened butter or mayo for brushing (optional)
6 slices provolone cheese

INSTRUCTIONS