Preheat oven to 400*F. Spray bottom of baking dish to prevent sticking. Place chicken breasts in dish, leaving room between to allow heat to circulate. Sprinkle chicken liberally with Greek Seasoning and let sit for 10 minutes. In a separate bowl, combine olives and sun-dried tomatoes. Divide olive/tomato combination into quarters. Top each chicken breast with one quarter of the olive/tomato mix (pile it high!). Drizzle lemon, zest and garlic on top of each. Layer one quarter of the spinach leaves on each chicken breast. Top each breast liberally with mozzarella cheese, ensuring entire breast is covered. Cover dish with foil, and bake at 400* approximately 15 minutes, remove foil and continue baking another 10 minutes or until chicken reaches an internal temperature of 165*F and juices run clear. Remove from oven, and let rest 10 minutes before serving.