Break up the cold rice with your fingers until no clumps remain. Toss the chicken with 1 tbsp soy sauce and the cornstarch. Beat the eggs with the salt, and have the scallions, garlic, ginger and frozen vegetables within reach of the stove.
Heat a 36 cm / 14-inch flat-bottomed wok over high heat for 1 minute, until a drop of water evaporates on contact. Add 1 tbsp oil and the chicken in a mostly single layer. Cook 4 to 5 minutes, stirring every 30 seconds, until browned and the largest piece reads 165 F / 74 C. Move it to a plate.
Lower the heat to medium-high and add 1 tbsp oil. Pour in half the beaten eggs and stir slowly for 30 to 45 seconds until they set in large soft curds. Move them to the plate with the chicken.
Add the last 1 tbsp oil, the scallion whites, garlic and ginger. Stir 30 seconds until fragrant, then add the peas and carrots and cook 2 minutes. Add the rice, press it against the wok and toss for 4 to 5 minutes, until the grains are hot, separate and a few have toasted edges.
Return the chicken and egg curds to the wok. Add the remaining 2 tbsp soy sauce, the sesame oil and the pepper. Push the rice to one side, pour the remaining beaten eggs into the cleared space and scramble 20 to 30 seconds until nearly set, then fold everything together and toss for 1 minute.
Taste and add a splash more soy sauce if needed. Scatter the scallion greens on top and serve right away.