Pat the halal beef chuck roast thoroughly dry on all sides using paper towels. Season aggressively all over with 1 tsp kosher salt, cracked black pepper, and garlic powder.

Heat olive oil in a large heavy skillet or Dutch oven over medium-high heat until shimmering hot. Sear the roast undisturbed for 4 to 5 minutes per side, including the narrow edges, until a deeply browned, caramelized crust forms. Transfer the seared roast into your slow cooker insert.

Add the onion wedges to the same hot skillet and sauté for 2 minutes to pick up the browned fond. Stir in tomato paste and smashed garlic for 1 minute until fragrant. Pour in beef broth, Worcestershire sauce, and balsamic vinegar, scraping up all flavorful browned bits from the pan bottom.

Arrange the halved potatoes and carrot chunks around and slightly under the seared beef in the slow cooker. Pour the hot savory broth mixture evenly over the beef and vegetables.

Tuck fresh rosemary sprigs, thyme sprigs, and bay leaves into the liquid. Cover with the lid and cook on LOW for 8 to 9 hours (or on HIGH for 4.5 to 5 hours) until the beef is fork-tender and shreds effortlessly.

Carefully transfer the tender roast, carrots, and potatoes to a warm serving platter and tent loosely with foil. Discard herb sprigs and bay leaves.

Skim excess fat from the surface of the slow cooker juices. Whisk the cornstarch and cold water slurry into the bubbling broth. Switch slow cooker to HIGH (or pour liquid into a saucepan over medium heat) and simmer for 5 to 8 minutes until thickened into a rich, velvety dark brown gravy.

Shred the roast into large rustic chunks using two forks. Ladle the hot savory gravy generously over the shredded beef, carrots, and potatoes. Garnish with chopped fresh parsley and serve hot.