Slice off top third of loaf; hollow out bottom section, reserving crumbs for another use. Spread inside surfaces of bread with butter. Place bread on a baking sheet, and bake at 400° for 8 minutes. Set aside.
Dredge oysters in cornmeal mix. Fry oysters, in batches, in deep hot oil (375°) 2 minutes or until oysters float to the top and are golden. Drain oysters well on paper towels; keep warm.
Combine mayonnaise and next 3 ingredients; stir well. Stir in lettuce. Spread lettuce mixture in hollowed bread. Top with tomato slices, oysters, and top of loaf. Cut loaf into 4 portions.