Sprinkle the steak with white pepper and sugar, toss to coat, let sit for 15 minutes.
Sprinkle the salt, cornflour and soy sauce into the steak. Stir to mix.
Heat a large frying pan with 1 tablespoon oil over high heat. Stir-fry the garlic and shallots until fragrant, 2-3 minutes. Add the steak and stir-fry until evenly browned, about 3-4 minutes. Add the soy sauce, stir and set aside.
Heat the same frying pan with 1 tablespoon oil over high heat. Stir-fry the onion and salt until soft, 3-4 minutes. Add the green pepper and stir-fry for 1 minute. Stir in the barbecue sauce, oyster sauce and steak. Serve.