Preheat the oven’s broiler and place a rack about 6 inches from the heat source.
Place tortilla on a work surface. Spread refried beans down the center; top with taco meat and onion.
Wrap the tortilla around the filling and place, seam-side down, in a small baking dish. Pour sauce evenly over the tortilla and top with cheese.
Broil until the cheese is melted and the sauce is bubbly around the edges, 1 to 2 minutes.
