Boil shells with tablespoon salt until fully tender. Drain, briefly cool-rinse, and drain thoroughly.

Whisk oil, vinegar, Dijon, dressing salt, and pepper in large bowl.

Gently fold in pasta, tomatoes, and well-drained mozzarella to coat.

Tear basil in just before serving; retoss. Serve cool or refrigerate without basil up to 24 hours, adding basil when ready.

Refrigerate leftovers within 2 hours.