Season beef with salt and pepper to taste. Heat a large nonstick skillet on medium-high. Spritz with cooking spray, then sear beef until nicely browned, about 2-3 minutes. Set aside.
In a 6-quart slow cooker, whisk together beef broth, tomato paste, Worcestershire sauce, vinegar, mustard, and all of the spices.
Add beef, potatoes, carrots, onion, and garlic to the slow cooker. Mix with the seasoned broth to coat the veggies and beef. Add in the two bay leaves.
Cover and cook on low or 7-8 hours, or on high for 3-4 hours--until the beef is tender and almost falling apart.
In a small bowl, whisk together 3 tablespoons of cornstarch with 3 tablespoons of water to create a slurry. Slowly stir the mixture into the slow cooker.
Cover and cook on high for another 10 minutes, or until thickened.
Turn off slow cooker and mix in peas. Let stand for a minute or two, just until peas thaw. Garnish with parsley, if desired.