Heat olive oil in a pot over medium heat. Sauté onions and garlic until tender.
Add carrots, celery, and cooked beef to the pot. Stir and cook for a few minutes.
Pour in the reduced-sodium beef broth and diced tomatoes with their juice.
Add green pepper, barley, Worcestershire sauce, dried thyme, beef gravy mix, and bay leaf. Stir well to combine.
If desired, add red wine for additional depth of flavor.
Bring the soup to a boil, then reduce the heat to low. Cover and simmer for 40-50 minutes or until the barley is tender, stirring occasionally.
Remove the bay leaf and discard.
Season with salt and pepper to taste.
Garnish with fresh parsley before serving.