In a large skillet, brown each roast in oil on all sides. Drain. Transfer meat to a 7-qt. slow cooker. Combine the water, onion, garlic, salad dressing and gravy mixes, pepper flakes, Italian seasoning and Worcestershire sauce; pour over beef. Cover and cook on low for 8-10 hours or until meat is tender.
Remove beef; cool slightly. Skim fat from cooking juices. Pour juices into a large bowl. Shred beef with 2 forks; add to bowl. Using a slotted spoon, place ½ cup on each bun. Top with cheese and giardiniera if desired.
