Preheat oven to 425 degrees F. In a 12-inch skillet cook beef, mushrooms, and onion over medium heat about 8 minutes or until beef is browned and onion is tender, stirring occasionally. Drain off fat. Stir in salt and pepper.
Meanwhile, grease a large baking sheet or line with parchment. Unroll pizza dough on baking sheet. Roll or pat dough into a 15x12-inch rectangle. Top dough with beef mixture, keeping filling within 1-1/2 inches of edges. Fold edges over the filling, pleating as needed.
Bake tart for 15 minutes or until crust is golden. Top with blue cheese and, if desired, oregano and pizza seasoning.