Spray 13x9-inch (3-quart) glass baking dish and 10-inch nonstick skillet with cooking spray. In skillet, cook ground turkey over medium-high heat, stirring frequently, until no longer pink. Remove turkey from skillet; drain on paper towels.
In large bowl, mix potatoes, onions, mushrooms, olives, 1 tablespoon basil and 2 cups of the cheese. Stir in turkey; spoon evenly into baking dish. Sprinkle with remaining 1 cup cheese.
In large bowl, beat eggs. Stir in milk and 1/2 teaspoon salt; pour over potato mixture in baking dish. Cut sheet of foil large enough to cover baking dish; spray with cooking spray. Cover baking dish with foil, sprayed side down. Refrigerate at least 8 hours or overnight.
When ready to bake, heat oven to 350°F. Bake covered 45 minutes. Uncover; bake 20 to 25 minutes longer or until center is set. Let stand 10 minutes before serving.
Meanwhile, spray 8-inch nonstick skillet with cooking spray. Add garlic; cook and stir over medium heat 1 minute. Stir in tomatoes and 1/4 teaspoon salt; cook about 5 minutes, stirring occasionally, until tomatoes are tender. Stir in 2 tablespoons basil.
To serve, cut egg bake into squares; serve with warm topping.