1. Marinate the Beef:

1. Prepare the Marinade:
   In a bowl, combine the beef strips with 3 tablespoons of soy sauce, 1/2 tablespoon of cornstarch, and 1 tablespoon of vegetable oil. Mix well to ensure the beef is evenly coated. Set aside to marinate for at least 15 minutes to tenderize and infuse the beef with flavor.

2. Prepare the Vegetables and Sauce:

1. Chop the Vegetables:
   Slice the green bell peppers and onion into thin strips. Mince the garlic cloves and grate or finely chop the ginger.
2. Make the Sauce:
   In a small bowl, mix 1 tablespoon of soy sauce, 1 teaspoon of oyster sauce, 1/2 tablespoon of cornstarch (dissolved in 2 tablespoons of water for a slurry), 100 ml of water, sugar, allspice, and a pinch of salt. Set aside.

3. Stir-Fry the Beef and Vegetables:

1. Heat the Oil:
   Heat 1 tablespoon of vegetable oil in a large wok or skillet over medium-high heat until hot.
2. Cook the Beef:
   Add the marinated beef to the wok in a single layer, and stir-fry for 3-5 minutes until it browns and is almost cooked through. Remove the beef from the wok and set aside.
3. Sauté the Aromatics and Vegetables:
   In the same wok, add the minced garlic, grated ginger, sliced onions, and bell peppers. Stir-fry for 3-4 minutes until the vegetables are tender-crisp and aromatic.

4. Combine and Finish the Dish:

1. Add the Beef Back In:
   Return the cooked beef to the wok with the vegetables, stirring to combine.
2. Pour in the Sauce:
   Give the sauce mixture a quick stir and pour it over the beef and vegetables. Cook for another 2-3 minutes, stirring constantly, until the sauce thickens and evenly coats the ingredients.
3. Adjust Seasoning:
   Taste and adjust salt, sugar, or additional soy sauce as needed.

5. Serve:

1. Plate and Enjoy:
   Serve the stir-fried beef and vegetables hot over a bed of steamed rice or noodles. Garnish with chopped green onions or sesame seeds if desired.