Pat the chicken cubes dry and toss in a bowl with cornstarch, salt, and black pepper until evenly coated.
Heat the neutral oil in a large wok or non-stick skillet over medium-high heat until shimmering.
Add the chicken in a single layer and sear without moving for 2 minutes to develop a crust, then toss and cook for another 3 minutes until crispy and cooked through. Remove chicken from the pan and set aside.
In the same pan, add the minced garlic and sauté for 30 seconds until fragrant but not browned.
Add the chilled rice to the pan, breaking up clumps with a spatula, and stir-fry for 3 minutes to dehydrate and toast the grains.
Push the rice to the perimeter of the pan to create a well in the center.
Pour the whisked eggs and egg whites into the center, scrambling them continuously until 80% set, then fold into the rice.
Return the crispy chicken to the pan along with the frozen peas and carrots.
Drizzle soy sauce and sesame oil over the mixture and toss vigorously for 2 minutes over high heat.
Remove from heat, garnish with sliced green onions, and serve immediately.