Begin by marinating the beef strips in a mixture of soy sauce and cornstarch, letting them sit for at least 15 minutes.

Heat a tablespoon of peanut oil in your preheated wok over high heat until shimmering.

Add sliced onions and cook for about 3-4 minutes, stirring frequently until they turn translucent and lightly brown.

Next, add the marinated beef strips to the wok and sear them for 3-5 minutes until they turn brown and are cooked through.

In the same wok, combine soy sauce, oyster sauce, minced garlic, and grated ginger, stirring well and cooking for 1-2 minutes.

Return the seared beef to the wok and add bell peppers. Stir-fry for another 2-3 minutes, ensuring the peppers remain crisp-tender.