Combine beef, soy sauce, salt, ground black pepper, cornstarch, and sesame oil. Mix all the ingredients until evenly distributed and marinade for at least 1 hour.
Heat a frying pan or wok and pour-in 3 tablespoons of cooking oil.
When the oil is hot enough, pan fry the marinated beef in medium heat until the outer part turns medium to dark brown (about 3 to 5 minutes per side).
Add water and simmer until the beef is tender.
Heat a separate pan or cooking pot then pour in the remaining 2 tablespoons of cooking oil.
When the oil is hot enough, sauté the garlic, onion, and ginger.
Add the sliced bitter gourd and stir fry for 5 to 8 minutes.
Turn off the heat and transfer to the pan with the tender beef. Stir and cook for 2 to 3 minutes more.
Transfer to a serving plate then serve.
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