Let's cook.
Cook the rotini pasta according to package directions until al dente. Drain well and rinse with cold water to stop the cooking process and cool the pasta. Set aside.
In a large bowl, whisk together the mayonnaise, basil pesto, lemon juice, and black pepper until smooth and well combined.
Add the cooked chicken, cooled pasta, halved cherry tomatoes, and diced red onion to the bowl with the dressing.
Gently toss all ingredients until everything is evenly coated with the creamy pesto dressing.
Stir in the grated Parmesan cheese.
Taste and adjust seasoning if necessary. Serve immediately or chill for at least 30 minutes for flavors to meld.
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