Pat the chuck roast dry with paper towels and season it on all sides with salt, pepper, and garlic powder.
Heat olive oil in a skillet over medium-high heat. Sear the roast for 2 to 3 minutes per side until browned.
Place the sliced onion, carrots, and potatoes in the bottom of the slow cooker. Add the minced garlic.
Set the roast on top of the vegetables.
In a small bowl, whisk together the beef broth, Worcestershire sauce, tomato paste, thyme, and rosemary. Pour the mixture over the roast.
Cover and cook on low for 8 to 9 hours or on high for 5 to 6 hours, until the meat is tender and easily pulls apart with a fork.
Remove the roast and vegetables carefully and place them on a serving platter.
In a small bowl, mix cornstarch and water. Stir it into the liquid in the slow cooker.
Cover and cook on high for another 10 to 15 minutes, or until the gravy thickens.
Serve the pot roast warm with the vegetables and spoon the gravy over the top.