How to Make It
Heat the olive oil in a large skillet. Add the garlic and crushed red pepper and cook over low heat until the garlic is golden, about 3 minutes. Add the tomatoes and their liquid and simmer over moderate heat, stirring occasionally, until slightly thickened, about 7 minutes. Add the tuna and simmer briefly to heat through; stir gently to keep the tuna in large pieces. Season with salt and black pepper and keep warm.
Cook the spaghetti in a large pot of boiling salted water, stirring occasionally, until al dente. Reserve 1/4 cup of the pasta cooking water. Drain the spaghetti and return it to the pot. Add the butter and toss well, then add the tuna sauce, reserved pasta cooking water and basil and toss again. Season with salt and black pepper, transfer to a warmed bowl and serve at once.