1. Preheat oven to 350°.
2. Combine first 5 ingredients in a large bowl; stir with a whisk. Set aside.
3. Punch Flatbread Dough down; cover and let rest 5 minutes. Divide dough into 2 equal portions. Working with one portion at a time (cover remaining dough), roll each half into a 12-inch circle on a floured surface. Place each dough circle on a baking sheet sprinkled with 1 tablespoon cornmeal. Brush each portion with 1 teaspoon oil, leaving a 1/2-inch border. Pierce entire surface liberally with a fork. Bake at 350° for 10 minutes or until crisp.
4. Add arugula, plums, and almonds to vinegar mixture; toss gently to coat.
5. Remove flatbreads to cutting board; top each with half of arugula mixture and 1/4 cup goat cheese. Cut each piadina in half.