Trim fat from roast and cut into 1 inch cubes. Place meat in a large pot over medium heat with oil, onion and garlic and cook, stirring, until meat is browned and onion is tender. Pour in broth, tomatoes and water. Stir in mixed vegetables, mushrooms and celery. Season with oregano, thyme, basil, parsley and cayenne. Bring to a boil, then reduce heat, cover and simmer 75 minutes.
Stir in pasta and cook 10 minutes more, until pasta is tender.