In a large skillet, heat over medium heat. Add the ground beef, cooking for 5-7 minutes until browned and crumbly. Stir occasionally and carefully drain any excess fat.

Add the finely diced onion and minced garlic to the skillet, stirring for 2-3 minutes until the onion softens and becomes translucent.

Stir in the shredded cabbage, mixing thoroughly with the beef mixture. Sauté for about 5 minutes, or until the cabbage becomes wilted yet retains a slight crunch.

Pour in the soy sauce, sesame oil, rice vinegar, ground ginger, and optional red pepper flakes. Mix well and cook for an additional 2-3 minutes.

Remove from heat and garnish with sliced green onions and toasted sesame seeds. Serve warm.