Cook the tortellini: Bring a large pot of salted water to a boil. Add the cheese tortellini and cook according to package directions, usually for about 3-5 minutes, until tender.
Drain and cool the pasta: Drain the cooked tortellini in a colander and rinse with cold water. This will stop the cooking process and cool the pasta down quickly for the salad.
Combine the ingredients: In a large serving bowl, gently combine the cooled tortellini, ¾ cup of basil pesto, 1 pint of halved cherry tomatoes, drained mozzarella balls, and ½ of a thinly sliced red onion.
Chill before serving: Cover the bowl and let the pasta salad chill in the refrigerator for at least 30 minutes to allow the flavors to meld together. Stir gently again before serving.
