In a large skillet or wok, heat the vegetable oil over medium-high heat. Add the ground beef and cook until browned, breaking it apart with a spatula, about 5-7 minutes. Drain excess fat if necessary.

Add the sliced onion, minced garlic, and ginger to the skillet. Sauté for about 2-3 minutes until the onion is translucent.

Stir in the shredded cabbage and cook for another 5-7 minutes, stirring occasionally, until the cabbage is tender.

Pour in the soy sauce and sesame oil, and sprinkle with red pepper flakes if using. Stir to combine and cook for an additional 2 minutes. Season with salt and pepper to taste.

Remove from heat and garnish with sliced green onions before serving.