Bring a large pot of salted water to a rolling boil. Add the fresh tortellini and cook until al dente, about 3-5 minutes. Drain and cool on a baking sheet, drizzling with olive oil.

Halve the cherry tomatoes and place in a mixing bowl. Finely chop the red onion, soak in cold water for 5 minutes, then drain and add to the tomatoes.

If making homemade pesto, blend basil leaves, olive oil, nuts, garlic, and Parmesan cheese until smooth. Mix well if using store-bought pesto.

In a mixing bowl, combine the cooled tortellini, tomatoes, onion, and mozzarella. Drizzle pesto over and toss gently until well mixed.

Fold in baby arugula and fresh basil leaves. Toss gently to incorporate without bruising the greens.

Serve immediately or refrigerate in an airtight container for 30 minutes to meld flavors.