At any of the buffets - just skip the items that don't fit your plan.
I often order an omelet at the sit-down breakfast restaurants and either give the "extras" to the other members of my party (usually DH) or I just ask the waiter/waitress not to bring them out. Sometimes they offer to add extra veggies as a substitute. That's nice, but it happens more often at lunch or dinner.
For something faster, I also bring my own high-fiber cereal & unsweetened soy milk, protein shakes, cheese and nuts, but we stay usually at one of the DVC resorts and so have a refrigerator.
Enjoy!