In a large Dutch oven, heat oil over medium-high heat. Season beef with salt and pepper, to taste. Working in batches, when the oil shimmers, add the beef and brown on all sides (it doesn’t need to be cooked through – just make sure it gets nice color on the outside) – about 10 minutes. Use a slotted spoon to remove the meat from the pot and set it aside (leave the fat in the pot).
Add the carrots, celery, and onion to the pot. Cook, stirring occasionally, for 10 minutes. Add mushrooms, garlic, and tomato paste and cook, stirring, for one more minute.
Stir in the tomatoes, rosemary, thyme, parsley, oregano, bay leaf, broth, and Worcestershire sauce. Scrape up all of the flavorful beef bits from the bottom of the pot as you stir! Return the beef to the pot, along with any accumulated juices from the plate. Stir in the potatoes. Season with ½ teaspoon salt and ¼ teaspoon pepper.
Increase the heat and bring soup to a boil. As soon as the soup boils, reduce the heat to low, cover, and simmer for 1 hour (or until beef is tender).
Stir in the green beans. Simmer for 5-10 more minutes, or until heated through. Discard bay leaf. Taste and season with additional salt and pepper, if necessary. Ladle into bowls and garnish with additional fresh herbs or crushed red pepper flakes, if desired.