Heat the oven to 350°F Cook the beef in a 10-inch skillet over medium-high heat until well browned, stirring often to separate meat. Pour off any fat. Stir the seasoning mix, beans, soup, onion and rice, if desired, in the skillet.
Divide the beef mixture among the tortillas. Roll up the tortillas and place seam-side down into a 3-quart shallow baking dish. Pour the enchilada sauce over the filled tortillas and sprinkle with the cheese.
Bake for 20 minutes or until the enchiladas are hot and bubbling.