Heat 1 tbsp of vegetable oil in a wok or large skillet over medium-high heat.
Add the sliced beef and cook until it is browned and cooked through, then remove the beef from the wok and set aside.
Add the remaining 1 tbsp of vegetable oil to the wok, and cook the onion, garlic, and sliced bell peppers until they are tender.
Return the cooked beef to the wok along with the soy sauce, oyster sauce, sugar, and black pepper. Stir fry together for 2-3 minutes, or until the sauce coats the ingredients and thickens slightly.
Adjust seasonings to taste, if necessary.
🍴 Serve and Enjoy!
Garnish with chopped green onions, and serve your simple beef stir fry with steamed white or brown rice for a delicious and satisfying meal. Enjoy!