Grease the bottom of a 13?x9? dish. Spread bread cubes on bottom of dish. Layer sausage or bacon on top of bread cubes. Then, top with cheese. In a bowl, whisk together eggs, milk, mustard, salt, and pepper. Pour over layered mixture in dish. Cover and refrigerate overnight. Preheat oven to 350 degrees F. Bake for about 45 minutes. Cool slightly before serving.