In a bowl, add the beef along with oyster sauce, brown sugar, soy sauce, fish sauce, grated garlic, baking soda, ground black pepper, and sesame oil. Marinate for 30 minutes or overnight for best results.
Heat a wok over high heat with 2 tablespoons of neutral oil and add the marinated beef. Sear for 30 seconds until the beef is seared, then toss for 2 minutes until the marinade is caramelized and the beef is done to your liking.
Add onion in another tablespoon of oil and stir fry until softened. Add back the beef, toss with the onions and enjoy.
Serve with sliced cucumbers, tomatoes and freshly steamed white rice if desired.
