Start by thoroughly cleaning the mussels and clams under running water. Ensure that any open clams or mussels are discarded.

In a large pot, heat a splash of olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.

Stir in the minced garlic and cook for another minute until fragrant.

Pour in the crushed tomatoes and the seafood stock. Allow it to simmer for about 5 minutes to amalgamate all the flavors.

Gently introduce the cleaned mussels and clams into the pot, followed by the shrimp and fish chunks. Sprinkle in the oregano, red pepper flakes, salt, and pepper.

Cover the pot and let the stew cook for about 10-15 minutes, or until the clams and mussels have opened, and the shrimp turn pink.

Once cooked, discard any unopened clams or mussels. Taste and adjust seasonings as needed.

Ladle the stew into bowls, garnish with freshly chopped parsley, and serve with crusty bread for dipping.