Bring a large pot of well-salted water to a rolling boil. Add the rotini and cook until al dente according to package directions. Do not overcook the pasta — it will absorb dressing as it chills and will soften further, so pulling it at true al dente is non-negotiable for the best final texture.

Drain the pasta thoroughly, then rinse it briefly with cold water to stop the cooking and bring the temperature down quickly. Several top-ranking recipes specifically call for cold rinsing here to prevent the warm pasta from melting the cheese or wilting the vegetables. Transfer to a large mixing bowl.

In a medium bowl, whisk together the Frank’s RedHot buffalo sauce, ranch dressing, mayonnaise, Greek yogurt, garlic powder, onion powder, celery salt, black pepper, and Dijon mustard until completely smooth and uniform. The dressing will be a vivid orange-pink color with a creamy, slightly thick consistency.

Taste the dressing before it hits the pasta. It should have a clear Buffalo heat up front, with a cooling, creamy ranch finish. If you want more heat, add another tablespoon of Frank’s. If you want it milder, increase the ranch or add a small spoonful of sour cream. This is the moment to get the balance right while you can still adjust it cleanly.

Add the shredded chicken, celery, carrots, red bell pepper, green bell pepper, and red onion to the bowl with the cooled pasta. Toss briefly to distribute evenly.

Pour the dressing over the entire mixture and toss well until every piece of pasta, every strip of chicken, and every vegetable is coated. The dressing should look like it is generously coating everything without pooling at the bottom of the bowl.

Add half of the blue cheese crumbles and all of the shredded mozzarella to the bowl and fold them in gently. The top results split between adding cheese fully mixed in versus sprinkling only on top before serving. The professional move is to do both: fold some in for built-in salty creaminess throughout, and reserve the rest to scatter over the top just before serving for a cleaner visual presentation.

Cover the bowl tightly and refrigerate for at least 30 minutes, or up to 1 hour for the best flavor. This chilling time is explicitly recommended in virtually every first-page recipe because it allows the pasta to absorb the buffalo ranch dressing and gives the vegetables time to soften very slightly and meld into the overall flavor.

Before serving, give the salad a final stir and taste for seasoning. Cold dishes consistently need a refresher — usually another pinch of salt, a small drizzle of buffalo sauce, or a squeeze of lemon juice to wake the whole dish back up after chilling. Scatter the remaining blue cheese crumbles and the sliced green onions over the top as a final garnish.