Place onions and carrots in a 5-quart slow cooker. Cut roast in half; add to slow cooker. In a small bowl, combine the soup, broth, mushrooms, thyme, Worcestershire sauce, rosemary, marjoram and pepper; pour over pork. Cover and cook on low for 5–6 hours or until meat is tender.
Remove pork to a serving platter; keep warm. Skim fat from cooking juices; transfer to a large saucepan. Bring liquid to a boil. Combine cornstarch and water until smooth; gradually stir into the pan. Bring to a boil; cook and stir for 2 minutes or until thickened.
Serve pork with gravy. Sprinkle servings with French-fried onions if desired.