Step 1: Heat 1 tablespoon of vegetable oil in a large wok or skillet over medium-high heat. Add the beaten eggs and cook, stirring, until scrambled and set. Remove the eggs from the wok and set aside.
Step 2: Add another 1 tablespoon of vegetable oil to the hot wok. Add the diced chicken and cook for 5-7 minutes, stirring occasionally, until browned and cooked through. Remove the chicken from the wok and set aside with the eggs.
Step 3: Add the remaining 1 tablespoon of vegetable oil to the wok. Add the diced onion and cook for 2-3 minutes until softened and translucent.
Step 4: Add the minced garlic and grated ginger (if using) to the wok. Cook for 1 minute until fragrant, being careful not to burn the garlic.
Step 5: Stir in the frozen peas and carrots (and corn, if using). Cook for 2-3 minutes, stirring, until the vegetables are tender-crisp.
Step 6: Add the cold, day-old rice to the wok. Break up any clumps with your spatula. Pour the soy sauce and oyster sauce (if using) evenly over the rice. Stir vigorously, tossing and folding the rice to coat it evenly with the sauce and vegetables. Cook for 3-5 minutes, allowing the rice to get slightly crispy and heated through.
Step 7: Return the cooked chicken and scrambled eggs to the wok. Toss everything together to combine. Stir in the toasted sesame oil and green onions. Cook for another minute to heat everything through. Taste and adjust seasoning with additional soy sauce or a pinch of salt and pepper if needed. Serve hot.