Mix the soy sauce, rice vinegar, garlic, granulated sugar, and five-spice powder in a medium bowl. Add the sliced pork tenderloin and gently toss to coat. Cover the bowl tightly with plastic wrap or a tight-fitting lid and refrigerate for at least 2 hours or up to 8 hours.
When you're ready to cook your fried rice, remove the pork from the marinade, draining as much of the excess liquid as possible. Discard the remaining marinade.
Heat two tablespoons of vegetable oil in a wok or large skillet set over medium-high to high heat. Once hot, add the pork to the pan and stir-fry until cooked, about 6-8 minutes.
Use a slotted spoon or spatula to remove the pork from the pan, setting it aside on a clean plate. Meanwhile, pour out any liquid from the pan and return it to medium-high heat.
Add the remaining two tablespoons of oil to the wok or skillet. Add the carrots and cook for 3-5 minutes or until tender. Add the peas, white parts of the onion, and garlic, and stir-fry for 3 minutes, stirring continuously.
Add the cold rice and stir-fry for approximately 6-8 minutes or until some rice starts to crisp (not burn). Remember to toss and stir often, and add a drizzle of oil if the rice starts to stick.
Form a well in the center of the rice and pour in the whisked eggs. Whisk the eggs until cooked, then stir it into the rice.
Meanwhile, mix the soy sauce, hoisin sauce, oyster sauce, and brown sugar in a medium bowl. Pour it over the rice and continue to stir fry for an additional 5 minutes or until the sauce is fully soaked in and the rice continues to crisp.
Stir in the cooked pork and green parts of the onions and heat for about 3 minutes.
Garnish with additional green onions and red pepper flakes, if desired.