Spray a 13 by 9-inch baking dish with nonstick cooking spray.
In a large skillet, cook the sausage over medium heat, stirring frequently, until browned and crumbly, about 10 minutes; drain well on paper towels.
Cut and discard the crusts from the bread. Cut the slices in half, and arrange in a single layer in the prepared baking dish, cutting pieces to fit as necessary to cover the bottom of the dish.
Sprinkle with the sausage and cheese.
In a large bowl, whisk together the eggs, milk, mustard, salt, and seasoned pepper; carefully pour the mixture over the cheese.
Bake casserole until set and golden, about 40 minutes. Let stand for 10 minutes before serving.
Notes
You can use diced ham instead of sausage.Don't use any bacon as it overpowers the entire dish.