If you're going to a sit-down joint, most will make some modifications to the standard plate if you ask. Instead of having your salad piled with croutons and cheese, you can ask to have them left off - maybe substitute with some additional fresh sliced veggies, and go for the balsamic vinaigrette or oil/vinegar dressing. Instead of rice or potato to go with that grilled chicken, ask for some veggies. Stuff like that.
On portions, the key is to eat what can fit in the palm of your hand.
2016 SGS CVO