Make sure not to overcook.
Rinse and pat chicken dry. Season with a little garlic powder and pepper and grill or pan sauté in 1/2 teaspoon oil in a medium oven-proof skillet, cooking until juices run clear. When done, shred chicken and set aside. Heat the remaining oil on medium. Add onions and bell pepper and sauté until soft. Add roasted peppers and season with a little salt and pepper. Add garlic and stir. Add tomatoes, parsley and shredded chicken. Pour egg whites over vegetable-chicken mixture, stirring vegetables with a spoon so egg covers bottom of skillet. Reduce heat to low and cook until bottom and sides of eggs are set, but center is still loose. Shake skillet occasionally to prevent sticking (about 5 minutes). To finish the omelet, preheat the broiler. Place skillet in broiler 6 inches from heat and cook until omelet is light golden (about 2 minutes). Be careful not to overcook. TO SERVE: Cool omelet slightly. Run knife around edge of pan to loosen. Invert omelet onto a plate.