1. Heat 1 tablespoon of sesame oil in a large skillet or wok over medium-high heat. Add the chicken pieces and season with a pinch of salt and pepper. Cook, stirring occasionally, until the chicken is browned and cooked through, about 5-7 minutes. Once cooked, remove the chicken from the skillet and set it aside on a clean plate.

2. Add the remaining 1 tablespoon of sesame oil to the same skillet. Add the chopped yellow onion and cook until softened, about 2-3 minutes. Stir in the minced garlic and grated ginger (if using) and cook for another minute until fragrant.

3. Add the frozen mixed vegetables and chopped bell pepper to the skillet. Cook, stirring frequently, for 3-5 minutes, until the vegetables are tender-crisp.

4. Push the vegetables to one side of the skillet. Add the chilled, cooked rice to the empty side, breaking up any clumps with your spatula. Let the rice heat through for 1-2 minutes without stirring, allowing it to get slightly crispy on the bottom. Then, stir the rice to combine it with the vegetables.

5. Pour the soy sauce and oyster sauce (if using) evenly over the rice and vegetables. Stir well to coat everything. Create a small well in the center of the rice mixture. Pour the lightly beaten eggs into this well and scramble them quickly with your spatula until just set. Once scrambled, mix the eggs into the rest of the fried rice.

6. Return the cooked chicken to the skillet and stir everything together until well combined and heated through. Taste and adjust seasoning with additional salt, pepper, or soy sauce if needed.

7. Divide the fried rice among serving plates. Garnish generously with sliced green onions before serving immediately.