Preheat oven to 400°.
Arrange bread cubes in a single layer on a baking sheet. Bake at 400° for 8 minutes or until toasted.
Heat a medium skillet over medium-high heat. Coat pan with cooking spray. Add sausage to pan; cook 6 minutes or until browned, stirring to crumble. Combine sausage, bread, and onions in a large bowl. Combine milk, cheese, eggs, and egg substitute in a medium bowl, stirring with a whisk. Add milk mixture to bread mixture, tossing to coat bread. Spoon mixture into a 2-quart baking dish coated with cooking spray. Cover and refrigerate 8 hours or overnight.
Preheat oven to 350°.
Uncover casserole. Bake at 350° for 50 minutes or until set and lightly browned. Sprinkle with parsley; serve immediately.
If you have a hard time finding a pacakge of raw turkey breakfast sausage, you can use a package of pre-cooked turkey sausage and just skip the step of browning the sausage in the skillet. Just put it in the skillet to heat it thoroughly.