In a large skillet, heat over medium-high heat and add the ground beef, breaking it apart with a spatula. Cook for about 5-7 minutes, stirring occasionally, until the beef is browned and no longer pink.

Carefully drain excess fat from the skillet, leaving a bit for added flavor. Add the diced onion to the skillet, stirring frequently for 3-4 minutes until the onions become golden and translucent.

Stir in the minced garlic and grated ginger, allowing them to cook for about 1-2 minutes until fragrant.

Add the shredded cabbage to the skillet, stirring well to combine with the beef mixture. Cook for 5-7 minutes, stirring occasionally until the cabbage wilts and softens yet retains a bit of crunch.

Mix together the soy sauce, sesame oil, rice vinegar, and optional red pepper flakes in a bowl. Pour this sauce over the beef and cabbage mixture, stirring to coat. Cook for another 2-3 minutes until heated through.

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