Sear the Beef (Optional, but Recommended): In a large skillet, heat 2 tablespoons of olive oil over medium-high heat. Pat the stewing beef dry, then sear it in batches until browned on all sides, about 5-6 minutes per batch. Transfer the seared beef to the slow cooker.
Prepare the Vegetables: In the same skillet, add the remaining tablespoon of olive oil. Sauté the diced onions, chopped bell pepper, carrots, and celery for about 5 minutes until they begin to soften. Add the minced garlic and tomato paste, cooking for another 2 minutes. Transfer the vegetables to the slow cooker.
Assemble the Soup: Add the beef broth, smoked paprika, dried thyme, garlic powder, onion powder, black pepper, and Seasoning Salt to the slow cooker. Stir to combine.
Cook: Cover the slow cooker and cook on low for 7-8 hours( or on high for 4-5 hours) until the beef is tender.
Add the Barley: About 1 hour before the end of the cooking time, stir in the pearl barley. Continue cooking until the barley is tender.
Finish and Serve: Once the cooking time is complete, taste the soup and adjust the seasoning if necessary. Stir in the chopped parsley. Ladle the soup into bowls and enjoy it warm.