Butter or spray a 9x11 inch baking dish with cooking spray. Layer bread, ham, cheeses.
Mix eggs, milk and salt in a medium bowl. Add garlic powder, salt, mustard, garlic powder and pepper. Slowly add the cheese, ham, bread, and salt. Place in the refrigerator overnight. Cover with foil.
Strain the contents of the refrigerator. Turn oven on to 350F. Cover the pan and bake for 30 minutes. Bake for another 15 to 20 minutes, turning off the foil.
Allow to cool in the oven for about 5-8 minutes before removing from the oven. You can keep it covered in the refrigerator for up to four days.