Crumble sausage into a medium nonstick skillet. Cook over medium heat until nicely browned, breaking up into bits with spatula as it cooks. Sprinkle with poultry seasoning.
Coat a 9 x 13-inch baking dish with cooking spray and set aside.
Add sausage to a large bowl along with toasted bread squares, cheese, mustard powder and salt, if desired. Set aside.
Add eggs and milk to a mixing bowl and beat on medium low speed until smooth and completely blended.
Drizzle egg mixture over the sausage and bread mixture. Stir to blend.
Pour into the prepared baking dish. Spread top evenly. Cover with foil and then chill in the refrigerator for 8 hours or overnight.
Preheat oven to 350° and bake covered for 45 minutes. Uncover and reduce the temperature to 325°. Bake an additional 10 minutes.