Heat the oil in a large casserole set over moderate heat. Add the onions, pepper, garlic and salt and pepper and cook the vegetables, stirring occasionally, for 5 minutes. Add the tomatoes, red wine, stock, tomato paste, 1/2 cup of the parsley, the rosemary, thyme and oregano, bay leaf, and red pepper flakes. Bring to a boil and simmer, covered, for 30 minutes.
Add the crabs, shrimp, halibut, and sea bass to the casserole and simmer, covered, for 15 minutes. Add the mussels, clams, and scallops and simmer. covered, for 10 minutes more, or until mussels, clams, and scallops open. Correct the seasoning adding lemon juice, salt and pepper to taste. Sprinkle with remaining parsley.