Remove crust from bread slices and lightly butter each side.
Place bread slices in 9x13 greased baking dish, to cover bottom.
Brown sausage with chopped onion, then drain.
Sprinkle sausage over bread.
Spread green chilies over sausage mixture.
Add Monterey Jack cheese on top of sausage mixture.
Add 1 teaspoon seasoned salt, 1 rounded teaspoon ground cumin, and 1 teaspoon dry mustard to 6 beaten eggs, then add half & half and mix well.
Pour egg mixture over sausage mixture.
Cover with foil and refrigerate overnight. You can freeze, at this point if you prefer. When ready to use put in refrigerator overnight to thaw.
Remove foil and bake at 350 degrees for 45 minutes or until lightly browned.