Combine last 11 ingredients in bowl. Spoon mixture over fish in heavy baking dish and cook over high heat about 15 minutes to reduce liquid, frequently shaking pan and stirring carefully. Arrange clams, shrimp and scallops around fish, then bake until clam shells open about 30 minutes. If all do not open, cover pan with foil and continue baking a few minutes longer; discard any that still have not opened. Spoon off as much liquid as possible into saucepan (tent fish with foil and keep warm) and simmer until reduced by about half. Arrange lemon slices on fish and pour reduced liquid over top.