Rinse mussels and clams under cold water; discard any with cracked shells or that do not close when tapped. Pull beards from mussels. Pat fish, shrimp, and calamari dry and cut fish into 1-inch pieces. Keep seafood chilled until ready to add.

Prepare aromatics

Finely chop the onion, celery, carrot, and red pepper (if using). Mince garlic. Zest the lemon and cut into wedges. Chop parsley and slice basil if using.

Make the base

Heat a wide, heavy-bottomed pot or Dutch oven over medium heat and add the olive oil. When oil shimmers, add the chopped onion, celery, and carrot. Cook, stirring occasionally, until softened and translucent, about 6–8 minutes.

Add the diced red pepper (if using) and minced garlic and cook 1–2 minutes more until fragrant, taking care not to let the garlic brown.

Stir in the crushed red pepper flakes and dried oregano; cook briefly to bloom the spices, about 30 seconds.

Pour in the white wine to deglaze, scraping any browned bits from the bottom of the pot. Increase heat slightly and simmer until the wine reduces by about half, 3–4 minutes.

Add the crushed tomatoes with their juices, the bay leaf, and the fish stock (or clam juice). Stir to combine, then bring the mixture to a gentle simmer. Reduce heat to maintain a low simmer and cook 12–15 minutes to meld flavors. Taste and season with about 1 tsp salt and 1/2 tsp black pepper, adjusting later as needed.

Cook the seafood

If the broth is too thick, add up to 1/2 cup water to reach desired consistency. Bring the broth back to a gentle simmer.

Add the firm white fish pieces first, simmer gently for 3 minutes.

Stir in the clams and mussels, cover the pot, and cook for 4–6 minutes until most shells have opened. Discard any shellfish that do not open.

Add the shrimp and calamari (if using) and cook uncovered just until the shrimp turn pink and opaque and calamari are tender, about 2–3 minutes more. Do not overcook.

Taste the broth and adjust seasoning with additional salt, pepper, or a pinch more red pepper flakes as desired. Remove and discard the bay leaf.

Finish & Serve

Off heat, stir in chopped parsley and basil and add a small splash of olive oil and a generous grating of lemon zest to brighten the stew. Gently stir to combine.

Ladle the stew into warmed bowls so each portion gets a mix of fish, shellfish, and broth. Serve with lemon wedges and crusty bread for dipping. Offer grated Parmigiano-Reggiano at the table for those who want it (use sparingly with seafood).

Leftovers: cool quickly, refrigerate in an airtight container up to 2 days. Reheat gently over low heat, adding a splash of water or stock if needed.