Preheat Oven To 350 Degrees F (175 Degrees C). Lightly Grease A Baking Sheet. In A Small Bowl, Mix Together Mayonnaise, Mustard, Horseradish, And Lemon Juice. Stir In 1/4 Cup Bread Crumbs And 1 Tablespoon Parmesan Cheese. Arrange Fish Fillets On The Prepared Baking Sheet. Spread Bread Crumb Mixture Evenly Over Fish. In A Small Bowl, Mix Together Melted Margarine, 1/4 Cup Bread Crumbs, And 1 Tablespoon Parmesan Cheese. Sprinkle Over The Coated Halibut. Bake For 15 To 18 Minutes, Or Until Fish Flakes Easily With A Fork.