1. In large mixing bowl, place egg, pizza sauce, salt, pepper and Kellogg's Corn Flakes® cereal. Beat until thoroughly combined. Add ground beef, onion and mushrooms. Mix lightly but thoroughly. Press half the meat mixture evenly in bottom of ungreased 8 x 8 x 2-inch pan. Place 2 slices of cheese over meat mixture. Press remaining meat mixture evenly over cheese.
2. Bake at 350° about 1 hour or until meat begins to shrink slightly from sides of pan (160 degrees F). Remove from oven.
3. Meanwhile cut remaining cheese into narrow strips. Lattice cheese strips diagonally over top of meat. Return pan to oven and continue baking about 3 minutes longer or until cheese strips are slightly melted. Cut into squares. Serve hot, garnished with parsley and sweet cherry peppers, if desired.