Prepare all ingredients by slicing the beef, cabbage, bell pepper, and onion. Mince the garlic and grate the ginger.
In a bowl, combine the soy sauce, oyster sauce, sesame oil, and cornstarch (if using); set aside.
Heat the vegetable oil in a large skillet or wok over medium-high heat.
Once hot, add the sliced beef and stir-fry for about 3-4 minutes until browned and cooked through. Remove the beef from the skillet and set aside.
In the same skillet, add the onion, bell pepper, garlic, and ginger. Stir-fry for about 2-3 minutes until the vegetables are slightly softened.
Add the shredded cabbage to the skillet and stir-fry for another 3-4 minutes until the cabbage is wilted.
Return the beef to the skillet and pour in the sauce mixture. Stir well to combine all ingredients and heat through for an additional 1-2 minutes. Season with salt and pepper to taste.
Serve hot over cooked rice or noodles.