In a large skillet, cook beef over medium heat until no longer pink, drain. Stir in taco seasoning and water. Bring to a boil. Reduce heat; simmer, concovered for 5 minutes.
Meanwhile, in a microwave safe bowl, combine the beans and salsa. Cover and microwave for 1-2 minutes or until spreadable. Place three tortillas in a greased round 2-1/2 quart baking dish. Layer with half of the beef, bean mixture, corn and cheese; repeat layers.
Bake, uncovered at 350 for 40-45 minutes or until cheese is melted. Let stand 5 minutes. Serve with lettuce, tomatoes, olives and sour cream if desired.