Preheat the oven to 350. Spray a 13x9 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 a 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, seasoned salt, and pepper. Carefully pour the mixture over the cheese.
Bake casserole until set and golden, about 40 minutes. Let stand for 10 minutes before serving.