Columbia Harbour House, Pinocchio Village Haus and Cosmic Rays all have salads at the MK; Sunshine Seasons at Epcot has a lot of different options that are healthy; we don't do counter service at the Studios and we only eat at Flame Tree Barbecue at Animal Kingdom (I think the pizza place there might have salads and sandwiches).
Sunshine Seasons has the best salmon and veggies! Of course, that's always offset by their awesome desserts, but it's certainly worth a stop. If you were familiar with the salmon at Tusker House when it was CS, it's very much like that.
Columbia Harbour House has a great sandwich--hummus and broccoli slaw on (I believe) whole grain bread. It is delicious and one of my musts on every trip.
The veggie chili at Columbia Harbour House is really, really good!
Me & DW order the cheese pizza/salad combo at Pinocchio's & order an extra side salad. Works out great for us.
You'll find a salad of some kind available at most of the CS locations in the parks.
WDW likes you to order combos--usually including fries with a sandwich. They will gladly substitute the yummy apple slices at most CS locations. You can also order the sandwich w/o the fries for about $1.80 less than the combo. We eat way too many of the delicious fries at Coronado Springs, so we try to stay away from them in the parks.