Iceburg lettuce is on the Do Not Feed list because it really has no nutritional value. I give fruit no more than once a month and I make sure they get a variety of veggies. I buy different veggies every week. My res love red, yellow and green peppers, carrots, turnip, grapes, banana, apple, romaine and red leaf lettuce and dandelion greens. They tend to stay away from chard and kale, I think because they have a bitter taste to them. You'll have to experiment to see what your turt likes. Mine used to love zucchini but now they won't go near it. They can be picky lil guys. Just be sure to mix it up...variety is key.
Oh, and welcome to the site

The things that come to those who wait may be the things that were left by those who got there first - Steven Tyler