Preheat oven to 400 degrees Fahrenheit. Cut zucchini, peppers, onion, and sweet potato into long, thin strips. Place on a greased cookie sheet, sprinkle with salt, and spray generously with cooking spray.

Bake for 40 minutes, stirring once halfway through. Let cool to room temperature and refrigerate until ready to use.

Combine dressing ingredients in a container and refrigerate until ready to use.

To assemble, right before serving, place some vegetables on each flatbread. Crumble some feta cheese on top. Drizzle with dressing.