First, put a large pot of water on to boil and salt it well.
Meanwhile, make your condimento: Get yourself a large bowl. (A wooden salad bowl is ideal here.)Take the garlic and rub the inside of the bowl vigorously with the cut ends of the garlic halves. (If you want a slightly more intense garlic flavor, leave them in the bowl and remove them just before you add your pasta. Otherwise discard them.)
Now break up the tuna into largish chunks and place in a large bowl. Add the capers, olives, red pepper flakes, parsley and olive oil to the bowl and very gingerly give it a turn or two to mix everything together, taking care not to break up the tuna fish too much. Taste and season lightly if it needs it.
When the water has come to a bowl, throw in the pasta and cook it until it is perfectly al dente. Drain the cooked pasta well and add it to the bowl, along with the basil leaves and a drizzle of colatura if using. Give everything another quick turn to mix—again, very gingerly to avoid breaking up the tuna.
Serve, topped with a sprinkle of parsley for color if you like.
