In a large mixing bowl, whisk together eggs, milk, dry mustard, garlic powder, salt and pepper.
Add cheese to egg mixture and stir to combine.
Place bread pieces into greased 9 x 13 inch baking pan. Sprinkle in ham and onions over the bread
Pour egg mixture over the bread, ham and onions, pressing the bread into the eggs to make sure it is all saturated.
Cover with plastic wrap and refrigerate overnight.
Bake, covered with foil, at 325℉ for 45 minutes, then remove foil and bake for an additional 15 minutes, until golden brown on top.
Notes
Nutrition Facts are just an estimate
Can also be prepared and then frozen after baking. Cover tightly and freeze for up to three months. Place in the refrigerator overnight to thaw and then bake at 325ºF for 30 minutes, covered, until cooked through.
If making the same day, make sure the bread is saturated and bake as directed.