Sear the roast: Heat olive oil in a large skillet over medium-high heat. Season the chuck roast evenly with salt, pepper, garlic powder, onion powder, thyme, and rosemary. Sear the roast for about 3–4 minutes per side until browned on all sides. This step helps build a deeper, richer flavor, so make sure each side develops a nice crust before moving on.

Prepare the slow cooker: Add the sliced onions and minced garlic to the bottom of the slow cooker. Layer the carrots and potatoes over the onions to create a base that will absorb the juices while cooking. Place the seared chuck roast on top of the vegetables so it stays elevated slightly above the liquid.

Add liquids and seasoning: In a mixing bowl, combine the beef broth, Worcestershire sauce, and tomato paste. Stir well until the tomato paste is fully dissolved and the mixture is smooth. Pour this liquid evenly over the roast and vegetables, ensuring everything is partially submerged to promote even cooking and tenderness.

Slow cook the roast: Cover with the lid and cook on low for 8 hours or on high for 4–5 hours, until the beef is fork-tender and easily pulls apart. Avoid opening the lid frequently during cooking, as this releases heat and can slow down the process.

Optional gravy thickening: Once the roast is done, carefully remove the beef and vegetables from the slow cooker and set them aside. In a small bowl, mix cornstarch with water to form a slurry, then stir it into the remaining cooking liquid. Let it cook on high for 5–10 minutes until the sauce thickens into a rich gravy consistency.

Serve the pot roast: Slice or shred the beef and arrange it with the vegetables on a serving platter. Spoon the warm gravy over the top and garnish with fresh parsley if desired. Serve hot for the best taste and texture.