Grease 13x9-inch (3-quart) baking dish. Using doughnut cutter, cut rings from each slice of bread; set bread rings aside. Tear remaining bread into pieces; place in greased baking dish. Arrange cheese slices over bread. Layer chicken, onion, broccoli and pimientos over cheese. Arrange bread rings over top.
In medium bowl, combine eggs, milk, salt and mustard; blend well. Pour egg mixture evenly over mixture in baking dish; sprinkle with paprika. Cover; refrigerate at least 4 hours or overnight.
Heat oven to 325°F. Uncover; bake 55 to 65 minutes or until knife inserted in center comes out clean. Let stand 10 minutes before serving.