Let dough rest at room temperature for 30 minutes. Preheat oven to 450°.
Stretch pizza dough into a 17×8-inch rectangle and transfer to a baking sheet. Spoon pimiento cheese on top of dough and spread using the back of a spoon or of set spatula, leaving a ½-inch border around edge. Sprinkle with spinach, bacon, and red onion.
Bake until cheese is bubbly and crust is golden brown, 10 to 15 minutes. Let rest for 2 minutes. Cut and serve warm with ranch dressing, if desired.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/cheesy-bacon-flatbread/