Preheat oven to 400° . Combine creamed spinach, Swiss cheese, water chestnuts, Parmesan cheese, mustard, salt and pepper in large bowl. Slice top off bread loaf; carefully remove soft bread from inside, leaving 1/2-inch thick shell. Cut top piece and soft bread into bite-size pieces. Store bread pieces in plastic bag or sealed plastic container to keep soft until ready to use. Spoon spinach mixture into shell; wrap loaf in foil, leaving filling exposed. Bake for 35 to 40 minutes, or until heated through. Serve warm with bread pieces for dipping.