Add the beef into a large ziplock bag. Set aside. In a medium bowl, whisk together the soy sauce, beef stock, red wine vinegar, ground ginger, minced garlic, cornstarch, and crushed red pepper flakes. Pour the mixture into the ziplock bag; seal and store in the refrigerator for at least 30 minutes.

While the beef is marinating in the refrigerator; add the oil, onion, and peppers into a large pan. Saute on low-heat until the onions and peppers have caramelized and are tender. Set aside.

In another large pan, remove the beef with a slotted spoon and cook under the beef is cooked. Add the beef to the pan with the onions and peppers, pour the marinate into the pan and simmer on low for 10 minutes.

Serve with rice and garnish with sesame seeds.