Cook the Ground Beef:
In a large skillet or wok, heat sesame oil over medium-high heat.
Add the ground beef and cook, breaking it up with a spoon, until browned and fully cooked (about 5-7 minutes). Drain any excess fat if necessary.

Add the Vegetables:
Add the diced onion and minced garlic to the pan with the cooked beef. Sauté for 2-3 minutes until softened and fragrant.

Stir-Fry the Cabbage:
Add the shredded cabbage to the skillet and stir well to combine with the beef and onion mixture. Cook for 5-7 minutes, stirring occasionally, until the cabbage is tender but still slightly crunchy.

Season the Stir-Fry:
Stir in soy sauce (or coconut aminos), rice vinegar, grated ginger, red pepper flakes (if using), and black pepper. Cook for another 2-3 minutes, allowing the flavors to meld.

Serve:
Remove from heat and garnish with chopped green onions and sesame seeds. Serve hot.