Heat the olive oil in a large skillet over medium-high heat.
Add the diced onion to the skillet and sauté for about 3 minutes until translucent.
Add the ground beef to the skillet, breaking it apart with a spatula. Cook for about 5-7 minutes, stirring occasionally, until the beef is browned and fully cooked.
Stir in the minced garlic, ground ginger, and black pepper, cooking for another minute until fragrant.
Add the sliced cabbage to the skillet and stir well. Cook for about 5 minutes, or until the cabbage is tender and wilted.
Pour in the soy sauce and oyster sauce (if using) over the mixture, stirring to incorporate all flavors evenly. Continue cooking for an additional 2-3 minutes.
Drizzle the sesame oil over the beef and cabbage mixture and stir to combine.
Remove from heat and garnish with chopped green onions before serving.