In a large skillet, heat over medium heat and add the ground beef. Cook for about 5-7 minutes, breaking it apart until no pink remains. Drain excess fat, leaving a small amount for flavor, then transfer beef to a plate and set aside.

In the same skillet, add the diced onion and minced garlic to the remaining fat. Sauté for 2-3 minutes until the onion becomes translucent and fragrant.

Stir in the shredded cabbage, mixing well with the onions and garlic. Sauté for about 5 minutes until the cabbage begins to wilt.

Pour in the soy sauce, sesame oil, rice vinegar, ground ginger, and red pepper flakes. Season with salt and pepper to taste, and continue to cook for another 2-3 minutes.

Once combined and the cabbage is tender, remove from heat. Plate the dish and garnish with green onions and sesame seeds if desired. Serve immediately.