Preheat oven to 375°. Grease bottom of 13×9 baking dish.
Combine beef, onion, and garlic in large skillet. Cook over medium-high heat, stirring occasionally, for 4-5 minutes or until beef is no longer pink. Stir in enchilada sauce and 1/2 c olives. Bring to a boil. Reduce heat to low, cover. Cook, stirring occasionally, for 5-8 minutes.
Layer tortillas, beef mixture, and cheese, repeat. Cover and bake for 20 minutes. Uncover, bake for an additional 5 minutes or until bubbly and cheese is melted. Sprinkle with remaining olives.