Cook the pasta in boiling salted water according to the instructions on the packet. Clean and wash the peppers and cut them into thin rings. Wash the basil, dab dry, put something aside for garnishing.
Pluck off the remaining leaves. Peel and finely chop the onion. Mix vinegar, salt and pepper. Whip the oil into the mixture. Drain tuna and cut into pieces. Pour the pasta onto a sieve, rinse with cold water and drain.
Mix all ingredients with the vinaigrette. Season to taste again. Pour the pasta salad into a bowl and garnish with basil.