Rinse the pearl barley in a fine-mesh strainer until the water runs mostly clear. Set a Dutch oven over medium heat and toast the damp barley, stirring, until lightly nutty and dry, 3 to 4 minutes. Transfer to a bowl.
Pat the beef dry, then season evenly with the kosher salt and black pepper. Let it stand at room temperature for 10 minutes while you dice the vegetables.
Return the pot to medium-high heat and add the olive oil. Sear the beef in 2 batches until well browned on most sides, 5 to 6 minutes total per batch. Transfer the browned beef to a plate; leave the drippings in the pot.
Reduce heat to medium. Add the onion, carrots, and celery with a pinch of salt and cook, stirring, until the vegetables soften and the onion turns translucent, 6 to 8 minutes.
Stir in the garlic and tomato paste and cook until the paste darkens to a brick-red color, about 2 minutes. Sprinkle in the dried oregano and add the Worcestershire; cook 30 seconds more to bloom the flavors.
Pour in 1 cup of the beef broth and scrape up the browned bits from the bottom. Return the beef and any juices to the pot, add the remaining broth and the bay leaf, and bring to a gentle simmer. Partially cover and cook, stirring occasionally and skimming any foam, until the beef is tender, 45 to 55 minutes.
Stir in the toasted barley. Simmer uncovered, stirring every few minutes so the grains don’t settle, until the barley is plump and tender, 25 to 30 minutes. If the soup gets thicker than you like, add hot water in small splashes to loosen.
Fish out the bay leaf. Taste and adjust seasoning with additional salt and pepper as needed. Take the pot off the heat and let it rest for 10 minutes to allow the barley to finish hydrating and the broth to settle.
Ladle into bowls and finish with chopped parsley.