Bring a large pot of generously salted water to a rolling boil. Add the linguine and cook according to package directions until al dente. Before draining, reserve about 1 cup of the starchy pasta water. Drain the linguine and set aside.

While the pasta is cooking, heat the olive oil in a large skillet over medium heat. Add the minced garlic, chopped anchovy fillets (if using), and red pepper flakes. Sauté for 2-3 minutes, stirring frequently, until the garlic is fragrant and the anchovies have dissolved into the oil.

Pour in the crushed tomatoes, then add the pitted and halved Kalamata olives and drained capers. Stir to combine. Bring the sauce to a gentle simmer, then reduce the heat to low, cover, and let it cook for 10-12 minutes, allowing the flavors to meld. Stir occasionally.

Uncover the sauce and gently fold in the drained and flaked tuna. Cook for another 2-3 minutes, just to warm the tuna through, being careful not to break it up too much. Taste and season with salt and freshly ground black pepper as needed (the olives, capers, and anchovies are quite salty, so taste first).

Add the drained linguine directly into the skillet with the tuna puttanesca sauce. Add about 1/4 cup of the reserved pasta water and toss vigorously to coat the pasta evenly, emulsifying the sauce. Add more pasta water a tablespoon at a time if the sauce seems too dry, until it reaches your desired consistency.

Stir in the fresh chopped parsley and lemon zest. Toss once more. Serve immediately in warm bowls, garnished with a little extra fresh parsley if desired.