Choose a tender cut of beef and cut it into bite-sized pieces. Marinate with cooking oil, a little seasoning powder, and oyster sauce for about 30 minutes.

Cut the onion and bell pepper into squares.

Heat cooking oil in a pan and add minced garlic. Sauté until fragrant. Add the beef and stir-fry until it just starts to brown, then remove from the pan.

Add the onion and bell pepper to the pan and stir-fry for 2-3 minutes. Return the beef to the pan and stir everything together. Season with black pepper, fish sauce, salt, and MSG to taste.