Cook the rotini pasta according to package directions until al dente. Drain the pasta and rinse under cold water to stop the cooking process. Allow the pasta to cool completely before assembling the salad.
While the pasta cools, chop the sun-dried tomatoes into bite-sized pieces. Slice the cherry tomatoes in half, thinly slice the red onion, and roughly chop the fresh basil.
If desired, lightly toast the pine nuts in a dry skillet over medium heat for 2 to 3 minutes. Stir frequently until lightly golden and fragrant. Allow them to cool before adding them to the salad.
In a small bowl, whisk together the olive oil, red wine vinegar, Dijon mustard, Italian seasoning, minced garlic, salt, and black pepper until the dressing is fully combined.
In a large mixing bowl, combine the cooled pasta, sun-dried tomatoes, cherry tomatoes, mozzarella pearls, red onion, basil, and pine nuts. Toss gently to distribute all ingredients evenly throughout the salad.
Pour the dressing over the pasta mixture and toss until everything is coated evenly. Make sure the dressing reaches all the pasta and vegetables for the best flavor.
Cover and refrigerate the salad for at least 30 minutes before serving. This resting time allows the flavors to blend and develop.
Before serving, toss the salad one final time and garnish with extra basil, mozzarella pearls, or freshly cracked black pepper if desired.