In a large pot, heat the olive oil over medium-high heat. Add the beef stew meat and brown on all sides, about 5-7 minutes. Remove the beef and set aside.
In the same pot, add the diced onion and garlic. Sauté until the onion is translucent, about 3-4 minutes.
Add the carrots, celery, and bell pepper to the pot. Cook for another 5 minutes, stirring occasionally.
Return the browned beef to the pot. Add the diced tomatoes, beef broth, water, thyme, oregano, bay leaf, salt, and pepper. Bring to a boil.
Reduce the heat to low, cover, and simmer for 1.5 to 2 hours, or until the beef is tender.
Stir in the frozen mixed vegetables and Worcestershire sauce. Cook for an additional 10-15 minutes until the vegetables are heated through.
Remove the bay leaf before serving. Ladle the soup into bowls and garnish with fresh parsley.