I have been asked to make this on many occasions by family, friends, and co-workers. This is a very customizable and forgiving recipe. You can add ingredients you like or delete the ones you don't like. The most important part is the bread and egg layer and allowing the egg to be absorbed by the bread.
Chop onions and saute' with a tablespoon of oil or non-stick spray, until translucent (clear or see-through). If you are added peppers and garlic saute with the onions.
Add ground turkey and cook until all the pink is gone. Take off the heat and allow to cool. If you can pick it up with your fingers it is cool enough.
In a 9 x 13" baking dish, spray dish with non-stick spray. Mince, cube, or tear into small pieces the bread into the baking dish. The bread does not have to be rock hard but if you have bread that is too hard to eat as a sandwich, will do. Or off the reduced baked goods rack of your bakery or grocer will work nicely.
In a medium size mixing bowl, break the eggs and whisk with the milk, and mustard. (If you don't like mustard or have a vinegar allergy it can be omitted; this is a very forgiving and easy to personalize dish). You may want to substitute dry mustard; about a 1/2 teaspoon.
Over the bread add a layer of shredded cheese (I have even added Parmesan before). Layer the sausage mixture, pour egg mixture over the top of sausage and bread. Add another layer of cheese.
Cover with plastic wrap and refrigerate for at least 30 minutes or overnight.
To Bake: Preheat over to 375 degrees. Remove plastic wrap and bake for 30 - 45 minutes, until the egg and bread layer is a firm-custard like consistency.