Add one tablespoon oil to a 12 inch skillet and heat over medium-high. Season beef with salt and pepper. Add beef to the pan and saute until browned, about 5-7 minutes. Transfer to the slow cooker.
Add remaining tablespoon of oil to the skillet and reduce heat to medium low. Add onion, garlic and thyme. Cook, stirring frequently, until onion is soft and translucent, about 3 minutes. Add tomato paste and cook for 1 minute, stirring constantly. Add wine and soy sauce and continue cooking until wine is almost completely evaporated, scraping the bottom of the pan to remove any brown bits that remain. Add chicken broth and bring to a simmer. Transfer mixture to the slow-cooker.
Add beef broth, bay leaf, potatoes, squash, parsnips or carrots and pearl barley to the slow-cooker. Cover and cook on high for 4 hours.
Remove beef from the slow cooker using a slotted spoon or tongs. Set aside to cool slightly. Shred into bite size pieces and return to the pot.
Add vinegar one teaspoon at a time, adding more if necessary. Season to taste with salt and pepper. Serve garnished with chopped fresh parsley.