Cook the pasta: Bring a large pot of salted water to a boil. Cook the gigli pasta according to package instructions until al dente. Drain and set aside to cool slightly.
Toast the pine nuts: While the pasta cooks, heat a small pan over medium heat. Toast the pine nuts with a little olive oil and seasoning of your choice (such as a pinch of salt, pepper, or Italian herbs). Stir occasionally to prevent burning, and toast for about 2-3 minutes until golden and fragrant. Set aside to cool.
Combine the ingredients: In a large bowl, combine the drained pasta, pesto, sun-dried tomatoes (including some of their oil), toasted pine nuts, and salt and pepper. Mix well, ensuring the pasta is evenly coated.
Adjust consistency: If the pasta seems a little dry, add extra olive oil or a splash of pasta cooking water to help loosen it up and coat everything evenly.
Add arugula: If serving immediately, stir in the arugula while the pasta is still warm. If you're serving the salad cold, allow the pasta to cool completely before adding the arugula to prevent wilting.
Serve: Enjoy as a side or main dish. This pasta salad can be served warm or cold.