In a large bowl, combine tortellini, cherry tomatoes, red onion, and mozzarella pearls.
In a small bowl, add olive oil, balsamic vinegar, Dijon mustard, garlic powder, kosher salt, and black pepper. Whisk until fully combined.
Pour the dressing over the tortellini mixture. Stir gently to coat everything evenly.
Refrigerate for about 1 hour before serving, if possible, for best flavor.
Garnish with fresh basil before serving.