Romaine is mostly fiber and water and very little nutrition. Fruits are high in sugar and acids that can kill off the bacteria an iguana needs for proper digestion.
Fresh dark leafy greens are the best staple food, things like collard, mustard, turnip and dandelion greens. Igs need a lot of variety in their diets with at least 2 types of greens, some sort of yellow veggie, and a few other vegetables in their salads every day. This is my favorite food chart for iguanas:
http://www.greenigsociety.org/foodchart.htm