olive oil, more parsley, parmesan cheese, black pepper, and more crushed red pepper for serving(optional)
Bring a large pot of heavily salted water to a boil and cook linguine according to directions until one minute before al dente.
Pat seafood dry with a paper towel. (If using frozen seafood, make sure it's completely defrosted.)
Heat the olive oil (2 tablespoons) in a large deep skillet or pot over medium heat. Add the seafood (16 oz.) and the crushed red pepper (1/2 -1 teaspoon) and sauté until seafood is cooked through, about 5-6 minutes (or if already cooked, heated through, about 3-4 minutes).
Add marinara sauce (24 oz.) and parsley (2 tablespoons, if using) to the seafood in the skillet and heat through. If it's ready before the pasta is done, turn off heat and cover to keep it warm.
When pasta is finished cooking to 1 minute before al dente, transfer it directly to the skillet with tongs, as well as 1/2 cup of the pasta cooking water, and toss to coat. Heat for about 1-2 more minutes, until the pasta is finished cooking to al dente and the sauce thickens and coats the pasta well (you can add more pasta water 1/4 cup at a time if it seems dry at all).
Serve with an extra drizzle of olive oil, parmesan cheese, parsley, black pepper, and more crushed red pepper if desired.
I used a 1-lb. bag of frozen mixed seafood with calamari, shrimp, mussels, and octopus to make this. You can use any kind of seafood you want, cooked or uncooked, fresh or frozen, but fish may flake apart a lot as you make the sauce (shellfish and calamari/octopus are more ideal for this reason). If using frozen, sure it's defrosted completely by leaving it in the fridge for 24 hours before cooking or by running cool water over the seafood in a colander or soaking in cool water until defrosted.
If you want an extra spicy version of this diavolo sauce, try using arrabbiata sauce (which is a spicy marinara sauce) instead of traditional marinara.
Seafood linguine fra diavolo is best served right away, but leftovers will stay good(and still taste great reheated) for about 2 days.
Some purists out there may argue that parmesan cheese is not traditionally served with seafood. I acknowledge this, and also say do whatever makes you happy (I love parmesan cheese with mine!).