Spread the caramelized onions evenly over the naan to within 1/4-inch of the edges. Distribute the sliced roast beef over the onions. Tear the cheese into strips and lay them over the roast beef. Slide the pizza into the oven directly on the rack using a pizza peel or heat-proof wide spatula. Bake for 8-10 minutes, or until the cheese is melted and golden brown in places and the beef and naan are hot all the way through. Sprinkle the parsley and/or green onions over the top and let rest for 3 minutes before slicing.