In a large pot over medium heat, heat oil. Add onion, celery, salt, pepper and cook, stirring occasionally, until softened, about 5-7 minutes. Add the minced garlic and red pepper flakes. Continue to cook, stirring constantly, until garlic is fragrant, 1 to 2 minutes.
Add tomato paste and oregano and cook, stirring, 1 minute. Now add wine, raise heat to medium-high, and cook until cooking liquid is reduced by half, 5 to 7 minutes.
Add tomatoes with their juice, bay leaves, clam juice, and stock. Bring to a boil, reduce to a simmer and cook, covered, for 25-30 minutes. Taste and adjust seasoning.
Add clams, shrimp, calamari and scallops.
Arrange the fish on top of the stew, cover, and simmer until the fish and shrimp are firm and opaque, about 5 minutes more. Discard bay leaves and stir in parsley.