Preheat oven to 350 degrees F (175 degrees C). In a medium skillet over medium high heat, cook the ground beef and onion until beef is evenly browned and onion is tender.
Prepare the enchilada sauce according to package directions. Pour 1/4 cup of the sauce into the bottom of a 9x13 inch baking dish.
On each flour tortilla, place an equal portion of the ground beef mixture and about 1 ounce of Cheddar cheese, reserving at least 1/2 cup of cheese. Then tightly roll the tortillas and place seam side down in the baking dish.
Pour the remaining sauce over the top of the enchiladas and sprinkle with the remaining cheese and olives.
Bake in a preheated oven for 20 minutes, or until the sauce is bubbly and cheese is thoroughly melted.