Coat a 9x13 w (3 inch sides) baking dish with butter or non stick spray. Arrange half the bread slices in the bottom of the dish. Top with half the amount of each: cream cheese, prosciutto, mozzarella, and tomatoes.
Finish layering with the other half of those ingredients, but this time, topping with the cheese rather than the tomatoes. Whisk together the eggs, half & half (or milk) salt and pepper. Pour mixture over layers; cover and chill for at least 2 hours or as long as over night. Remove from the refrigerator 20 - 30 min. before baking. Bake strata at 350 degrees until puffed, golden brown and lightly set in the center...about an hour. Allow strata to rest for 10 min. before cutting