1. Cook farfalle according to package directions. Drain, rinse under cold water and drain again.
2. Drain tuna and transfer to a small bowl. Break into rough chunks, drizzle with 1 tablespoon oil and toss gently.
3. In a large bowl, whisk together lemon zest and juice, remaining oil, garlic, mustard, sugar, salt and pepper.
4. Add farfalle, beans, tomatoes, arugula and onion to bowl; toss well to combine. Add tuna; toss gently. Divide among 4 plates; top each serving with 1 teaspoon Parmesan.