1. Cook pasta as per packet directions, then drain.
  2. Meanwhile, heat oil in a large nonstick skillet over medium-high heat. Add the garlic and cook, stirring until fragrant, about 1 minute. Add anchovies (if using) and crushed red chilli pepper and cook for 30 seconds more.
  3. Add tomatoes, reduce the heat to medium, and cook, stirring occasionally for 8 minutes. Stir in tuna and cook until it is incorporated into the sauce and heated through, about 2 minutes.
  4. Divide the spaghetti evenly among 4 plates, top with sauce and garnish with basil.