Preheat oven to 375°.
Heat 1 tablespoon butter in a large skillet over medium heat. Add garlic and mushrooms; cook 6 to 7 minutes or until liquid evaporates, stirring frequently. Stir in herbs de Provence, salt, and pepper; cook 1 minute. Spoon into a large bowl. Set aside, and keep warm. Heat remaining butter in same pan. Add spinach; cook 2 minutes or until spinach wilts, stirring frequently. Stir spinach into mushroom mixture.
Place bread in a 13 x 9-inch baking dish coated with cooking spray. Drain excess liquid from spinach and mushroom mixture; spoon over bread.
Combine milk, eggs, egg whites, and provolone cheese, stirring with a whisk. Pour egg mixture over spinach and mushroom mixture. Top with Parmesan cheese.
Bake at 375° for 35 minutes or until set. Let stand 5 minutes before serving.