Preheat oven to 350°. In a large skillet, cook and crumble beef over medium heat until no longer pink; drain. Add beans, onion and taco seasoning. , Unroll crescent roll dough. Press onto bottom and up the sides of a greased 13x9-in. baking dish; seal seams and perforations. , Spread beef mixture over crust; sprinkle with cheeses. Bake, uncovered, until golden brown, about 30 minutes. If desired, sprinkle with toppings.