Step 1

Cook pasta in a large pot of generously salted water until al dente. Reserve 1 1/2 cups pasta water; drain.

Step 2

Heat a large skillet over medium heat. Add tuna with its oil and garlic and cook, stirring a few times, until garlic is golden in spots, about 5 minutes. Stir in capers and pepper flakes and cook, 30 seconds. Add 1 cup reserved pasta water; bring to a simmer. Add cooked pasta and simmer, tossing a few times, until liquid is reduced to a sauce that coats pasta.

Step 3

Remove from heat and toss in lemon zest and juice, oil, and parsley; season with pepper. Add more pasta water, a few tablespoons at a time, until pasta is evenly coated. Serve, sprinkled with more pepper flakes.