In a slow cooker, add the beef stock, brown sugar, soy sauce, Worcestershire sauce, olive oil, dry mustard, garlic powder, sesame seeds, ginger, and ground black pepper. Mix well.
Add the sliced chuck roast around the slow cooker so the meat is spread evenly and coated with the sauce.
Cover and cook on low for 4-5 hours or until the beef reaches 165 degrees F. Don’t overcook it as it will start to shred and not keep the slice shape.
Once the meat is cooked, put cornstarch in a small bowl and add 3-4 tablespoons of broth. Mix to create a slurry.
Add the mixture to the slow cooker. Mix well.
Add the frozen broccoli to the slow cooker. Mix well.
Cover and cook for an additional 10-15 minutes or until the broccoli is cooked to your liking.