Heat oven to 350 degrees. Brown ground beef with onion and garlic in large nonstick skillet over medium heat 8–10 minutes or until beef is not pink, breaking up beef into small crumbles. Pour off drippings, if necessary. Add taco sauce, cumin, salt, and pepper; cook and stir 1–2 minutes or until mixture is heated through. Place phyllo shells on rimmed baking sheet. Spoon beef mixture evenly into shells. Top evenly with cheese. Bake 9–10 minutes or until shells are crisp and cheese is melted. Top tarts with lettuce, tomatoes, guacamole, sour cream, and olives, as desired.