In a large skillet over medium heat, brown the ground beef until fully cooked. Drain any excess fat.
Add the diced onion and garlic to the beef. Cook for 2-3 minutes until fragrant and soft.
Stir in the shredded cabbage and sauté until slightly wilted, about 5 minutes.
Add soy sauce, sesame oil, rice vinegar, ground ginger, red pepper flakes, salt, and pepper. Mix well and cook another 2-3 minutes until cabbage is tender.
Garnish with sliced green onions and sesame seeds before serving.
Notes
Store leftovers in an airtight container in the refrigerator for up to three days. Reheat in a skillet over medium heat. For longer storage, freeze portions in freezer-safe containers for up to a month.