Preheat oven to 180°C (350°F). Spray a 9 x 9 x 2 inch (23 x 23 x 5 cm) baking pan with cooking spray. Arrange bread slices in pan overlapping slightly and set aside.
Beat together eggs, milk, bacon and 1/4 cup (50 mL) cheese in large bowl. Add mushrooms and salt. Pour mixture over bread slices. Sprinkle potatoes and remaining cheese over egg mixture. Bake until lightly browned and knife inserted near centre comes out clean, about 35 minutes. Serve immediately.