- Start by cutting the chicken breasts into bite-sized pieces. Season with salt and black pepper. 
- In a mixing bowl, combine the soy sauce, oyster sauce, sugar, and additional black pepper. Set aside. 
- Heat the vegetable oil in a frying pan or wok over medium-high heat. 
- Add the chicken pieces to the pan. Stir-fry for about 5-7 minutes, or until the chicken is golden brown and cooked through. Remove the chicken from the pan and set aside. 
- In the same pan, add the sliced onions, garlic, and ginger. Sauté for 2 minutes until fragrant. 
- Add the sliced bell peppers and continue to stir-fry for another 2-3 minutes. 
- Return the cooked chicken to the pan and pour in the prepared sauce. Mix everything together and cook for an additional 2-3 minutes, allowing the flavors to meld. 
- Taste and adjust seasoning if necessary. Remove from heat. 
- Serve hot, garnished with chopped green onions.