Prepare the Beef: Season the sliced beef with a pinch of salt and ground black pepper. Set aside while you prepare the other ingredients.

Heat the Oil and Sauté Aromatics: In a large skillet or wok, heat the olive oil over medium-high heat. Add the chopped onion and minced garlic, sautéing for about 1–2 minutes until fragrant and slightly softened.

Cook the Beef: Add the seasoned beef to the skillet. Cook for 3-4 minutes, stirring occasionally, until the beef is browned on all sides and almost fully cooked.

Add the Sauces: Pour in the soy sauce and optional oyster sauce, stirring to coat the beef evenly. If the mixture appears too dry, add the beef broth or water for added moisture.

Incorporate Spinach: Add the chopped spinach to the skillet and cook, stirring constantly, until it wilts and combines with the beef. This should take about 2–3 minutes.

Season and Finish: Drizzle with sesame oil if using, and adjust salt and pepper to taste.

Serve: Transfer to a serving dish and enjoy hot as a main course or side. This dish is the perfect complement to a serving of steamed rice or noodles.