Since all the ingredients are often served separately, you can choose exactly what goes in your fajita. The meats and vegetables are most often grilled. The only thing to check on is if the restaurant sautes the vegetables in oil. If so, ask if there is a way to cook them without oil.
Grilled foods can be high in carcinogens due to exposure to an open flame.
Ask your waiter if they are truly grilled or just cooked and made to look grilled. Lettuce, tomatoes and other vegetables can be added along with lots of flavorful, non fat salsa. It is better to order a la carte if possible. If not, choose one of the three sides offered. A full dinner can be enough calories and fat for at least two meals.