Preheat a large skillet over medium high heat. Add one tablespoon of oil. Working in batches, add beef to the pan and brown on all sides, about 30 seconds per side. Don't crowd the pan. Add the beef to the slow cooker as it gets browned. Repeat with remaining pieces of beef.
Once you have finished browning the beef, add lemon juice to the pan to help deglaze the pan. Using a wooden spoon, scrape up all the browned bits on the pan and add to the slow cooker. This is the flavor.
Add the pearl onions, red potatoes, and carrots to the slow cooker with the beef. Give a quick stir to combine and evenly distribute.
Pour the beef broth over the beef and vegetables.
Stir in the salt, tomato paste, minced garlic, bay leaves, and fresh thyme.
Cook on the low setting for 6-7 hours or high for 3-4 hours. You want the beef to be tender and easily shredded. Lightly shred the beef with two forks in the slow cooker. I don't like mine completely shredded and like to make sure there are still big chunks.
In a small bowl, combine tapioca starch (or cornstarch) with water or beef broth. Whisk until there are no clumps. Pour into the slow cooker and stir to combine. Let cook an additional 30 minutes to thicken the soup.
Serve with a sprig of fresh thyme or over mashed potatoes for a complete meal.