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 1/2 cup on each bun. Top with cheese and giardiniera if desired. Freeze option: Cool meat and juices; transfer to freezer containers. Freeze for up to 3 months. To use, thaw in the refrigerator overnight. Place in a Dutch oven; heat through. Using a slotted spoon, place 1/2 cup on each bun. Top with cheese and giardiniera if desired.