Marinate the chicken by mixing it with soy sauce, cornstarch, sesame oil, and white pepper. Let it sit for at least 10 minutes.
Prepare the sauce by whisking together soy sauce, oyster sauce, dark soy sauce, sugar, and white pepper.
Break up the day-old rice until it's fluffy and free of clumps.
Heat the wok or cast iron skillet on high for 2 minutes, then add 1 tbsp oil and the marinated chicken. Sear for 2 minutes without stirring.
Stir-fry the chicken until fully cooked, then remove it from the pan.
Add ½ tbsp oil to the pan, pour in the eggs, and scramble them, then set aside with the chicken.
Add the remaining vegetable oil and stir-fry the onions and green onion whites until softened. Add the garlic and peas and carrots, cooking for another minute.
Add the broken-up rice, spreading it out in the pan and pressing it down. Let it sit undisturbed for a minute, then stir-fry for 2-3 minutes.
Pour the sauce over the rice and toss to coat. Stir-fry for another minute.
Fold in the chicken and scrambled eggs, heating everything through. Drizzle with sesame oil before serving.
Serve hot, garnished with green onion tops.