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 2-3 minutes until the onion is translucent.

Stir in the chopped cabbage and cook for another 5 minutes, stirring frequently, until the cabbage is wilted and tender.

Pour in the soy sauce, oyster sauce, and sesame oil. Add red pepper flakes if using. Mix well 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.