Begin by seasoning the beef chuck roast with salt and black pepper on all sides. If you prefer, you can sear the roast in a large skillet with olive oil over medium-high heat for 3-4 minutes on each side until browned.
Place the seasoned roast in the slow cooker. If you used a skillet, transfer the roast directly after searing.
In a bowl, combine the onion soup mix, beef broth, minced garlic, and Worcestershire sauce (if using). Pour this mixture over the roast.
Scatter the sliced onion on top of the beef in the slow cooker.
Cover the slow cooker and set it to low heat for 8 hours. If you're short on time, you can set it to high heat for about 4 hours instead.
Once the cooking time is done, carefully remove the roast from the slow cooker. Let it rest for a few minutes before slicing it to serve.
Use a serving spoon to scoop out the gravy and onions to drizzle over the sliced steak.
Garnish with fresh parsley before serving for a touch of color.