Cut 12 rounds from bread and set aside. Take scraps of bread and fit into bottom of greased 13X9 inch pan.
Place 2/3 of the shredded cheese over bread, then all the broccoli (or spinach, squeezed dry), then all of the meat.
Place bread rounds on top. Combine milk, salt, mustard, and beaten eggs. Pour over contents in casserole.
Cover and refrigerate at least 6 hours (or up to 24 hours).
Bake uncovered at 325 degrees for 55 to 70 minutes.
Sprinkle the remainder of the cheese on top after the first 45 minutes.