1. In a small bowl, beat the egg whites.
2. In a 10-inch nonstick skillet, warm ½ teaspoon of oil on medium-low heat. Add half of beaten egg whites and spread evenly in a thin layer. Cover and cook for about 1 minute. Transfer the cooked egg white in a plate.
3. Repeat with the remaining egg whites.
4. In the same skillet, heat remaining oil on medium heat. Add onion and sauté for about 1 minute. Add chicken and remaining vegetables except avocado and cook for about 2 to 3 minutes.
5. In a bowl, beat egg yolks and add into skillet. Stir well like a scramble for about 3 to 4 minutes. Stir in avocado and remove from heat.
6. Place the chicken mixture on egg whites. Roll like burritos and serve.