Heat 2 tablespoons of oil in a large pan over medium high heat. Place the chicken in a bowl with the corn starch and toss to coat. Season the chicken pieces with salt and pepper to taste.
Place the chicken in a single layer in the pan. Cook for 3-4 minutes per side or until chicken is browned and cooked through. You may need to work in batches.
Remove the chicken from the pan and cover with foil to keep warm.
Add 1 teaspoon of oil to the pan, along with the onion and carrots. Cook for 4-5 minutes or until veggies are softened.
Add the garlic and cook for 30 seconds.
Remove the vegetables from the pan, then cover with foil to keep warm.
Pour the remaining teaspoon of oil into the pan; add the eggs and cook, stirring occasionally and breaking up with a spatula, until the eggs are scrambled and cooked through. Season the eggs with salt and pepper.
Add the rice, chicken, and reserved cooked veggies to the pan. Stir in the fish sauce, soy sauce and sugar, and mix gently until everything is thoroughly combined and warmed through, 3-4 minutes.
Sprinkle green onions over the top of the rice mixture, then serve. Garnish with cilantro leaves, sliced cucumber and tomatoes.