Stir tuna, capers and lemon zest into the sauce. Add drained spaghetti and a generous drizzle of olive oil, and toss well to combine. Add more salt, pepper and/or red pepper flakes as needed.
Add the tuna and cook together for 1 minute more. Season with a little salt and lots of ground black pepper. Drain the pasta and add to the tomato and tuna sauce. Toss together until well combined ...