Preheat oven to 325°F. Place flour in a shallow dish. Dip steak in flour to coat both sides, shaking off excess. Place in the bottom of a Dutch oven or large covered baking dish sprayed with cooking spray.
Add tomatoes (with juices), onion, celery, carrots, mushrooms, rosemary, thyme, Worcestershire sauce, beef broth, salt, pepper, and garlic powder.
Cover tightly and bake for 2 hours.
Stir together cornstarch and cold water to make a slurry.
Remove pot from oven and stir in cornstarch mixture. Cover and bake for 45 to 60 more minutes, until beef is fork-tender and gravy has thickened.
Remove herb stems. Slice or shred steak and serve with vegetables and gravy over mashed potatoes, noodles, or rice.