Cook the pasta according to the package instructions until al dente. Drain and spread it in a shallow dish to cool, tossing occasionally.
While the pasta cools, chop the bell pepper, cherry tomatoes, shallot, cucumber, olives, and sun-dried tomatoes into bite-sized pieces.
Transfer the cooled pasta to a large bowl. Add the chopped vegetables, drained tuna, and crumbled feta, and toss gently.
In a small bowl, whisk together the pesto, mustard, lemon juice, olive oil, wine vinegar, black pepper, and salt.
Pour the dressing over the salad and toss gently until evenly coated.
Garnish with fresh basil. Serve immediately or cover and refrigerate until ready to eat.