In A Large Bowl, Beat The Cream Cheese, Mayonnaise And Mustard Until Smooth. Stir In The Shrimp, Crab, 1/3 Cup Monterey Jack Cheese And Onions. Cut The Top Fourth Off The Loaf Of Bread; Carefully Hollow Out Bottom, Leaving A 1/2-In. Shell. Cube Removed Bread; Set Aside. Spoon Seafood Mixture Into Bread Shell. Sprinkle With Remaining Cheese. Wrap Tightly In Heavy-Duty Foil And Place On A Baking Sheet. Bake At 350