- Sprinkle beef with salt and pepper; coat evenly with flour, pressing lightly so it adheres.
- Heat oil in medium Dutch oven over medium heat. Add beef and cook until browned on all sides, about 10 minutes; transfer to plate. Add onions to pot and cook, stirring, until softened, about 5 minutes. Add half of garlic and cook, stirring, until fragrant, about 30 seconds.
- Add mushrooms, tomatoes, and wine to Dutch oven; cook, scraping up browned bits from bottom of pot, about 3 minutes. Increase heat and bring to boil; reduce heat and simmer until mushrooms are softened, about 5 minutes. Return beef and any accumulated juices to pot; reduce heat and simmer, covered, stirring occasionally and turning beef every 30 minutes, until beef is fork-tender, about 2 hours. Transfer beef to cutting board.
- Bring vegetable mixture to boil over medium-high heat; boil, stirring frequently, until reduced to 4 cups, about 12 minutes.
- Meanwhile, to make gremolata, stir together parsley, lemon zest, and remaining garlic in small bowl. Cut beef on diagonal into 12 slices. Serve sprinkled with gremolata and accompanied by vegetables with sauce.
- Per serving: 2 slices beef, generous 2/3 cup vegetables with sauce, and 1 1/2 tablespoons gremolata
Make it ahead. Prepare the pot roast through step 5, but do not make the gremolata. Transfer the beef and sauce to one or two airtight containers and refrigerate up to 4 days or freeze up to 3 months. To reheat, if frozen, thaw the meat and sauce in the refrigerator overnight. Transfer to large skillet. Cook, covered, over medium-low heat until heated through, about 10 minutes. Prepare the gremolata.