Cook the spaghetti
Bring a large pot of salted water to the boil. Add the spaghetti and cook according to the packet instructions until al dente.
Prepare the sauce
Peel and chop the onion and garlic cloves. Slice the chili. Place a large frying pan over a medium–high heat, add olive oil, onion and garlic. Cook for about 2 minutes, then add the chili, olives, capers, anchovy fillets and cook for about a minute. Chop half of the parsley, add it to the frying pan. Add the tomato passata and cook for about 5 minutes.
Drain the pasta, reserving about 50ml of cooking water. Add the pasta to the sauce, stir to combine and add the cooking water if necessary. Season with salt and pepper if needed. Transfer to serving bowls, top with the rest of the parsley, lemon zest and mozzarella (optionally). Enjoy