Cut tuna into one-inch cubes. Place the tuna in a medium pot and cover with olive oil. Add salt, chili flakes, thyme, and salt. Wrap peppercorns in sachet of cheesecloth and add to the oil. Bring oil to a simmer and cook over low heat for 20 minutes, stirring occasionally until tuna is cooked through. Remove tuna from the heat and cool.
Bring 6 quarts water to a boil and add 2 tablespoons salt. Cook the pasta according to the package directions, until al dente.
Meanwhile, in a sauté pan, add the tarantello, scallions, garlic, and a drizzle of olive oil. Sauté until tuna is warm and the garlic begins to toast. Carefully add one tablespoon of pasta water and butter. When the butter is melted remove cooked pasta from the water and add to the pan. Cook pasta in the pan for one minute. Remove from heat, add Parsley, and toss to mix all ingredients. Place on serving dish. Sprinkle with parsley and a pinch of chili flakes.