Heat olive oil over medium heat in a large, deep, ovenproof skillet. Add ground beef. Crumble and cook the beef until browned. Stir in onions and cook another 1-2 minutes or until soft. Stir in Worcestershire sauce, thyme, basil and salt. Add orzo to skillet and cover with beef broth.
Bring broth to a boil and then reduce heat and simmer until the liquid has been absorbed, about 12-15 minutes. Stir in mustard and pickles.
Preheat broiler. Place skillet under broiler for just a minute or until cheese has melted. Remove and top with freshly chopped tomatoes.