Pat the chuck roast dry. Season with salt, pepper, garlic powder, onion powder, and thyme. If using, lightly dust with flour.
Heat olive oil in a skillet over medium-high heat. Sear the roast for 3 to 4 minutes per side until browned.
Add onion, carrots, and potatoes to the bottom of a slow cooker. Sprinkle minced garlic over the vegetables.
Place the roast on top of the vegetables.
Whisk together beef broth, Worcestershire sauce, and tomato paste. Pour around the roast. Add the bay leaf. Dot butter over the top.
Cover and cook on LOW for 8 to 9 hours, until the roast pulls apart easily with a fork.
Transfer roast to a cutting board and rest 10 minutes. Move vegetables to a serving dish.
Pour cooking liquid into a saucepan and remove bay leaf. Bring to a gentle simmer.
Whisk cornstarch with cold water. Slowly whisk into simmering liquid and cook 2 to 4 minutes until thickened.
Slice or pull the roast into chunks. Serve with vegetables and spoon gravy over everything. Garnish with parsley if desired.