Combine the fish sauce and thinly sliced chili in a small bowl and set aside.
Heat the vegetable oil in a very hot large skillet or wok over high heat.
Crack the eggs into the skillet and scramble until just cooked, then push them to one side of the pan.
Add the chopped chicken to the skillet and stir-fry until mostly cooked through, then add the chopped onion, chopped tomato, and frozen peas and carrots; stir and cook until the chicken is done and vegetables are heated through.
Add the cold cooked rice, sugar, black pepper, soy sauce, and the reserved fish sauce with chili; stir continuously until the rice is heated, dry, and slightly glossy.
Taste and adjust seasoning if desired, then remove from heat and garnish with Thai basil, green onion tops, and/or cilantro before serving.
