Step 1Bring a large pot of liberally salted water to a rolling boil and add the spaghetti. Meanwhile, chop the tuna (you should have about 1 cup); set aside.
Step 2Heat the fresh olive oil in a large skillet over medium heat. When the oil is hot, add the garlic, chiles and fennel. Saute, stirring frequently, until the garlic is lightly golden and the spices are fragrant, 2 to 3 minutes.
Step 3Add the cherry tomatoes and the anchovies and cook for about a minute to break down the anchovies. Add the tuna and use a wooden spoon to break up the tuna and the tomatoes into a chunky mixture. Add the reserved tuna oil, red wine vinegar and salt to taste. The flavor should be sweet, fragrant and bright. Keep warm over low heat until the pasta is done.
Step 4When the spaghetti is done, drain it, reserving about 1 cup of the cooking water, and add the noodles to the skillet. Turn the heat to high, add the reserved pasta cooking water and cook, tossing the noodles to coat lightly with the sauce. Toss in the basil, season to taste with salt and serve immediately.