Heat sesame oil in a large skillet over medium-high heat.
Add the diced onion and cook for 2-3 minutes until translucent.
Stir in the garlic and ginger and cook for 1 more minute until fragrant.
Add the ground beef and cook until browned, breaking it apart with a spatula.
Drain excess grease if needed.
Stir in the coleslaw mix, soy sauce, rice vinegar, and black pepper.
Cook for another 5-7 minutes, stirring occasionally, until the cabbage is tender.
Serve hot, garnished with green onions and sesame seeds if desired.