Sprinkle the steak with white pepper and sugar, toss to coat and let sit for 15 minutes.
Sprinkle the salt, cornflour and soy sauce onto the steak. Stir to mix.
Heat a large frying pan with 1 tablespoon oil over high heat. Stir fry the garlic and eschallot 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 capsicum and stir fry for 1 minute. Stir in the barbecue sauce, oyster sauce and steak. Serve.