Scatter sliced onion in the bottom of a slow cooker, then alternately layer carrots and potatoes.
Heat oil in a large skillet over medium heat and season London broil with Creole seasoning. Sear beef in hot oil until well browned, 3 to 5 minutes per side. Transfer meat the slow cooker.
Pour beef broth, cream of mushroom soup, and red wine into the skillet used to cook the beef and bring to a simmer. Scrape any brown bits from the bottom of the skillet with a spatula. Pour broth mixture over beef.
Cook on Low for 8 to 10 hours or cook on High for 6 hours.