Pat the prawns dry with paper towels and season with a pinch of salt and the white pepper.
Heat 1 tbsp of the oil in a 12-inch / 30 cm wok or nonstick skillet over high heat. Add the prawns in a single layer and sear for 2 to 3 minutes, flipping once, until pink and opaque with an internal temp of 145 F / 63 C. Transfer to a plate.
Whisk the eggs and egg whites together in a small bowl. Add 1 tsp of oil to the pan, pour in the eggs, and scramble for about 1 minute until just set into soft curds. Transfer to the plate with the prawns.
Add the remaining 2 tbsp oil to the pan with the garlic and scallion whites. Stir-fry for 30 seconds until fragrant, don't let the garlic brown.
Add the cold rice, breaking up clumps with the spatula. Stir-fry for 3 to 4 minutes, pressing the rice into the pan occasionally, until heated through and a few grains turn light golden at the edges.
Push the rice to one side, add the frozen peas and carrots to the empty space, and cook for 1 to 2 minutes until thawed and warmed through. Stir them into the rice.
Return the prawns and eggs to the pan. Add the soy sauce and oyster sauce, and toss everything for 1 to 2 minutes until the rice takes on an even light brown color.
Drizzle in the sesame oil and toss once more. Taste and add extra salt if needed.
Scatter the scallion greens over the top and serve immediately, straight from the pan.