In a large skillet, cook ground beef over medium heat until no longer pink; drain.
Stir in enchilada sauce and salsa; set aside.
Place one tortilla in the middle of a greased 13×9-in. baking dish. Using a knife or kitchen scissors, trim one side off 2 other tortillas so that they fit on the edges of the baking dish without sticking up. Place them, slightly overlapping, on top of the tortilla in the center. Take the tortilla trimmings and place them in the corners.
Cover the tortillas with one-third of the meat mixture; top with half of the bag of frozen spinach and half of the can of olive slices; sprinkle with 1/3 of the cheese.
Repeat layers of tortillas, meat, spinach, olives, and cheese one more time.
Place a third layer of tortillas down followed by the last third of meat mixture. Follow this with the last third of the cheese.
Now that your casserole is built, bake uncovered for 25 minutes or until bubbly. Remove the casserole and let sit for 8 minutes before serving.
