In a large skillet, heat the oil over medium high. Add the beef and sprinkle with 1 teaspoon salt and pepper. Brown the beef on all sides, disturbing it as little as possible on each side so that it develops nice coloring. Once the beef is lightly browned (it won’t be all the way cooked through), remove it to a 6-quart slow cooker.
To the pan, add the onion. Cook and stir until the onion is beginning to soften, about 3 minutes. Stir in the garlic and let cook 30 seconds. Splash in about 1/2 cup the beef broth and scrape up any browned bits that have stuck to the bottom (this is flavor!). Let the broth reduce for 2 minutes, then transfer the entire mixture to the slow cooker.
To the slow cooker, add the carrots, potatoes, parsnips, and celery.
Add the diced tomatoes in their juices, tomato sauce, tomato paste, Worcestershire, oregano, paprika, sugar, 2 1/2 cups beef broth, and remaining 1 teaspoon salt.
Cover and cook on low for 8 hours, until the beef and vegetables are tender. Stir in the peas, just until warmed through. If the soup is thicker than you would like, add the remaining 1 cup beef broth until you reach your desired consistency. Serve hot, sprinkled with fresh parsley.
TO STORE: Store soup in an airtight storage container in the refrigerator for up to 4 days.
TO REHEAT: Gently rewarm leftovers in a large pot on the stovetop over medium-low heat, adding splashes of broth as needed as needed. You can also reheat this soup in the microwave until hot.
TO FREEZE: Place leftovers in an airtight freezer-safe storage container in the freezer for up to 3 months. Let thaw overnight in the refrigerator before reheating.