Trim any excess fat from the beef chuck roast and cut into bite-size pieces. Season with salt and pepper all over, to taste.
Add oil to a large skillet and heat over medium-high heat. Once hot, add in the beef, working in batches so you don't overcrowd the pan. Sear the beef on all sides, for about 3 minutes, until nice and browned.
Add the beef to the slow cooker, along with the onion, potatoes, carrots and celery.
In a large measuring cup or bowl, whisk together the beef broth, garlic, tomato paste, Worcestershire sauce and thyme. Pour over the beef and vegetables and add the bay leaf on top. Cook on LOW for 6 to 7 hours, or HIGH for 3 to 4 hours.
20 minutes prior to finishing, remove the bay leaf from the slow cooker. Combine the cornstarch and 3 tbsp water in a small dish and pour into beef stew, then stir to combine. Add in the frozen peas and cover again. Once peas are heated through and gravy has thickened, you are ready to garnish with fresh parsley and enjoy!