Step 1: Prepare the Beef

1. Thinly slice the beef against the grain into bite-sized strips.
2. In a bowl, combine the soy sauce, cornstarch, baking soda, Shaoxing wine, and sesame oil to make the marinade. Add the beef slices and mix well. Let the beef marinate for at least 15 minutes while you prepare the other ingredients.

Step 2: Mix the Sauce

1. In a small bowl, whisk together the soy sauce, oyster sauce, hoisin sauce, sugar, ground white pepper, and water. Set aside.

Step 3: Cook the Beef

1. Heat 2 tablespoons of vegetable oil in a large wok or skillet over high heat.
2. Add the marinated beef in a single layer and sear for 1-2 minutes on each side until browned. Avoid overcrowding the pan; cook in batches if necessary. Remove the beef from the pan and set aside.

Step 4: Sauté the Onions and Aromatics

1. Add the remaining 1 tablespoon of oil to the pan.
2. Sauté the onions for 3-4 minutes until they start to caramelize and soften. If using bell peppers, add them at this stage.
3. Add the minced garlic and ginger, and cook for another 30 seconds until fragrant.

Step 5: Combine and Serve

1. Return the cooked beef to the pan and pour the sauce over the top. Toss everything together and cook for 2-3 minutes, allowing the sauce to thicken and coat the beef and onions.
2. Taste and adjust seasoning if needed.
3. Garnish with chopped scallions and sesame seeds, if desired. Serve hot over steamed rice or noodles.