Lightly spray a 9x13" casserole dish with non stick cooking spray. Arrange the bread slices evenly out in the baking dish, breaking up extra pieces to fill in any gaps.
In a small mixing bowl, add the cream cheese, mayo, and Italian seasoning. Stir the mixture together until evenly incorporated.
Spoon the cheese mixture over the bread in dollops until it's all used. Use a spatula, or the back of a spoon, to spread the cheese mixture evenly out over the bread. Sprinkle the 1/2 cup of Parmesan evenly out over the top.
In a separate mixing bowl, toss together the meatballs and the sauce until well coated.
Spoon the the meatball mixture evenly out over the casserole, including all sauce. Sprinkle the remaining cheese evenly out over the top.
Bake the casserole at 350 degrees for 30-35 degrees, or until golden brown & bubbly.