This is actually three (or four) separate recipes. Make the caramelized onions and roasted tomatoes ahead of time. The flatbreads will go together quickly for a tasty appetizer, snack, or light meal.
Dough
Toppings
To make the flatbread ahead, cook each one until done in a cast iron skillet and store in a plastic container in the refrigerator. When ready to use, coat both sides with olive oil, top and bake until hot in the preheated oven.