Place sliced onions onto the grill. Cook until browned, 3-5 minutes per side. Slice and reserve for later use.
Meanwhile, dust a cutting board and rolling pin with flour. Divide the dough into 4 parts. Roll each part into a long, thin rectangle. Drizzle one side with olive oil. Place onto grill, drizzle other side with more oil. Cook for 2-3 minutes or until lightly charred. Flip to other side.
Quickly top the flatbread with steak, onions, and blue cheese. Close the lid and cook for 3-4 minutes, or until cheese just starts to melt and bottom crust is charred.
Slice each flatbread into 4 servings and top with arugula. Serve and enjoy!
Recipe by This Cookin' Dad at http://thiscookindad.com/2015/06/grilled-flatbreads/