Heat the olive oil in a large skillet over medium-high heat. Season the beef chuck roast with salt, pepper, garlic powder, onion powder, thyme, and rosemary. Sear the roast in the skillet for about 4-5 minutes on each side until browned. This step adds depth of flavor.
Place the chopped onions, carrots, and potatoes in the bottom of the slow cooker. Lay the seared roast on top of the vegetables.
In a separate bowl, mix the beef broth and Worcestershire sauce. Pour the mixture over the roast and vegetables in the slow cooker.
Cover and cook on low for 8-10 hours or on high for 4-6 hours, until the meat is tender and easily shreds with a fork.
If you prefer a thicker gravy, mix the cornstarch and water in a small bowl until smooth. About 30 minutes before serving, stir this mixture into the slow cooker and let it cook uncovered until thickened.
Once done, remove the roast and vegetables from the slow cooker. Let the roast rest for a few minutes before slicing. Serve with the gravy poured over the top.