Heat oil in a large pot or Dutch oven over medium heat. Sauté onion and bell pepper until soft, about 5 minutes.
Add garlic, oregano, thyme, crushed red pepper flakes, cayenne pepper, salt and black pepper. Cook for an additional 2 to 3 minutes, until garlic is soft.
Stir in wine, tomatoes, stock or broth, tomato paste, bay leaf and reserved clam juice. Bring to a boil; reduce heat to medium-low and simmer until flavors have blended, about 15 minutes.
Stir in clams and mussels. Reduce heat to low, cover with lid and cook until mussels are just beginning to open, about 4 minutes.
Add in white fish, shrimp and scallops. Stir gently to combine.
Increase heat to medium and simmer until seafood is cooked through and mussels have fully opened, about 5 minutes. Discard any unopened mussels.
Stir in parsley and serve immediately.